New Toy: HP 143 Wide-Screen Oscilloscope Mainframe Restoration – [Part 1]

Posted on August 14, 2014 by retrovoltage

At the risk of becoming a test equipment collector, I am picking up a few pieces of vintage test equipment that need some work, but will be very useful pieces of shop gear as well as interesting pieces of history lately. I’m needing a high speed analog X-Y monitor for some more complex alignments, and this old HP 143A oscilloscope came up on the local Craigslist for only a little more than the cost of the gas to drive and pick it up.

This is a really old school, transitional piece of gear. The CRT and mainframe assembly boasts all-transistor design, but the plug-in modules themselves are a mixture of tube, transitional nuvistor, transistors depending on the circuit position and the module’s capability.

They’re fairly rare, too, from what I can figure. A high school student in a family of engineers has one; a gentleman who did happen to be local had one earlier this year, and one configured with spectrum analyzer plugins is for sale reportedly removed from a Department of Defense HF monitoring station – a true cold war relic.

These wide-screen mainframes were a big ticket item back in the day, found in the HP scope catalog:

Adjusted for inflation, that’s very nearly a $10,000 CRT display – and don’t forget the options!

With what I’d consider the “base package”, add another $3,700 for the vertical amplifier and $3,100 for the timebase, you’re up to $17,000 for the instrument as shown below:

And the price only goes up from there! The mainframe supports some very high sensitivity (50 uV/div), differential, and high speed (GHz+) plugins – not to mention a frequency response generator, TDR, and spectrum analyzer that only go up get more expensive.

I’m lucky – all the knobs and switches are present. Those frequently get lost.

The HP Archive has good information about the scope including the operation manual and schematics. The plugins slide out easily:

Inside the timebase plugin, lots going on. Transistors and nuvistors together on this double-sided etched and silkscreened board:

Tubes on the other side of the enclosure, right next to some TO-92 package transistors.

Nuvistors were a very late-game evolution of the vacuum tube, and arguably held off the full transistor revolution for a few years.

Vintage really is beautiful.

This mainframe powers on successfully but doesn’t show a meaningful trace; it’s got some minor damage inside but should come back together nicely.

The vertical amplifier is pretty interesting inside, too:

This one has a mix of transistors, noval miniature tubes, and compactrons.

I’m looking forward to getting this one going again, but doubt I’ll be able to work on it before the end of the year.

Because this mainframe has identical vertical and horizontal amplifiers, the way to make it into an X-Y display is to use “vertical” amplifiers in both bays. If you have an HP 1402A plug-in for sale (or really, any other 1400-series HP plug-in), I’d love to hear about it.

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Close-Up of a Magic Eye

Posted on August 7, 2014 by retrovoltage

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The Speaker Spotter – Speakers of Craigslist – April 18th, 2014

Posted on April 18, 2014 by retrovoltage

There’s always something interesting for sale on Craigslist, especially in Seattle. Do click the titles to see the original postings with more photos and additional information if you’re interested – otherwise, enjoy the virtual window shopping! Rain City Audio is not affiliated with any of these sales; contact the respective sellers for more information. If it’s deleted, it’s probably sold already.

Avid Corporation 100 Speakers – $60 in Auburn

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Made to compete with the Advents out in the same era, these 1974 speakers feature a 10″ woofer in an acoustic suspension cabinet and a CTS phenolic ring tweeter for the high-end. That’s a pretty common driver configuration on early/mid ’70s high-end speakers. The woofers on these feature a butyl rubber surround, rather than foam, so it will never rot. They’re likely due for a crossover refresh after 40 years, though.

Dynaco A25 Speakers – $175 in Edmonds

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These Dynaco speakers are from the very early ’70s and have a very understated styling. They feature a 10″ woofer and 1.5″ tweeter in an aperiodic enclosure. These are towards the entry level of Dynaco’s model line, but are very well regarded. Here’s a great page with some information about that speaker family.

Bose 601 Series III Speakers – $650 in Everett

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I have a set of Bose 601 Series I speakers, and the design is virtually unchanged between the Series I and the Series III. The port is moved and the cabinet styling is slightly different with the sloped top, but the basic configuration is identical – two 8″ woofers and four 2″ tweeters in a direct/reflecting array mounted on top. These speakers are sensitive to room position, but are very life-like and musical – almost as good as the 901s.

Klangbox/Telefunken RB66 Speakers – $225 in Edmonds

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I can’t find much info about these on the Internet. They’re 4 Ohm speakers that will accept up to 20W of input power, and looks like there might be a 6″ or 8″ round driver and a 6×9″ driver under there. Telefunken equipment is interesting and fairly well regarded; these 1967 Telefunken speakers might be worth something. It wouldn’t surprise me if there’s only a few pairs of these around this country.

Fisher 15″ Speakers – $50 in Bonney Lake

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The Fisher name had a good pedigree at the beginning of the hi-fi era but were trending downwards by the ’80s. These were a high end model, though, with 15″ cloth/rubber woofers for good bass response. The pricing is realistic and they can get pretty loud – great garage or man-cave speakers. I do like the styling of the high-end pedastal cabinet Fishers like these.

Dahlquist M-905 Speakers – $275 in Everett

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These bookshelf/satellite Dahlquists are a bit smaller than the massive DQ-10s but can deliver great sound nonetheless, and these come with their original packaging and a set of 16″ speaker stands to sweeten the deal. These would make a good desktop speaker system, or compliment your home theater.

Vintage Heathkit AS-18 Speakers – $200 in Redmond

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From the late ’60s or early ’70s, these speakers were produced by Heathkit for the hi-fi enthusiast who also enjoyed DIY projects. Visually, they look similar to most other early ’70s speakers – but this model is special as the drivers are all Electro-Voice drivers. These are occasionally compared with the EV-7 speakers. Definitely unusual, and they probably sound great, especially when paired with a tube anp!

Vintage Pair of Realistic Nova-6 Speakers – $30 in Belltown

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Another speaker from the mod ’70s, back when Radio Shack/Realistic did make good hi-fi products, these Nova-6 lattice grill speakers take up to 45W. They’d go great with a period amp like a Harman/Kardon 430 and would make a killer vintage system.

Technics 7000A Speakers – $650 

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Technics is usually made a lot of low-end gear – but they produced some very interesting and innovative top-of-the-line models like these 7000A speakers. They’re a 3-way design with a 14″ woofer and time-aligned mid-range and tweeters and level controls on the top end. They look pretty impressive, too. I’m not impressed with their frequency response curve, but I’m very curious what these sound like.

Seeburg Discotheque DDS1 Speakers – $500 in University Place

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From the late ’60s, these Seeburg speakers – from the company more well-known for jukeboxes – were used in live sound environments. They’re basically Altec Lansing VOTTs in a different cabinet, with two 15″ Altec woofers and the exponential multi-cell horn and driver. Extremely accurate and efficient, I bet these sound absolutely fantastic – and that’s a killer price. I’d buy them if I didn’t already have enough speakers!

If you’re in the market for some new speakers, please click through to the sale ads and contact the sellers! Good luck!

Other Issues of the Speaker Spotter

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1931 Westinghouse WR-8 Columaire Antique Radio Repair

Posted on April 14, 2014 by retrovoltage

I recently got to work on another beautifully reconditioned Westinghouse WR-8 Columaire radio all the way from Bellingham. It was originally in for service with the SPARK Museum, but the repair technician reportedly suffered some health complications and was unable to complete the job so it came down to Seattle for me to finish. I’d previously worked on one of these back in 2013, but this one was in a bit better shape – although it took a long road to get there!

At some point in the past, the radio was badly damaged by an errant candle placed on top which must have fallen over and badly burned the top half of the radio. Afterwards, it was placed in a basement for many years and forgotten about, collecting moisture damage and dust along the way until being brought back out.

The owners spent a lot of time on the cabinet:

and reconing the speaker:

Then it was into the shop for the detailed electrical repairs!

All of the tubes in this radio tested brand new, and all the transformers and coils checked out, so it should be a pretty straightforward repair. Overwhelmingly, the resistors tested in spec also, only a few were slated for replacement. It’s been worked on before at one point, too:

An interstage transformer, normally potted in a top can, was replaced with an open-frame transformer from the late ’30s or ’40s, mounted under the chassis.

This model could be used with a phonograph or a remote control, although neither option was fitted on this model.

I began by mounting new terminal strips under the chassis, soldering them to the lugs on the old capacitor pack.

I took a slightly different approach for the other capacitor pack, using the existing phenolic board as the terminal strip after cutting off the pack capacitor.

For a size comparison, here’s a third capacitor pack containing only a single capacitor – and on top, its replacement, and a quarter for scale.

The owner requested something to make it easier to reset the clock when the time came: Molex connectors! I use 600V connectors with individual connections.

Not the prettiest, but it’ll work. The wire insulation was nicked in a few places, so I reinforced those areas with electrical tape.

Time to fire it up and test—loud and clear! I peaked up the alignment carefully and let it burn in for a while. The lead routing ultimately needed to be tweaked a little bit as there was some interference, but it was easily corrected.

After refitting both chassis and the speaker back into the cabinet, this Westinghouse was ready to go home and make warm, rich, beautiful music for many years to come.

What a beautiful piece! You’d never know how far it had to come to get to this shape. Bringing it back to life so nicely was a joint effort – without the owner’s dedication to the cosmetics of the cabinet, it would never have made it to the electrical stage.

 

 

 

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The Speaker Spotter – Speakers of Craigslist – April 11th, 2014

Posted on April 11, 2014 by retrovoltage

There’s always something interesting for sale on Craigslist, especially in Seattle. Do click the titles to see the original postings with more photos and additional information if you’re interested – otherwise, enjoy the virtual window shopping! Rain City Audio is not affiliated with any of these sales; contact the respective sellers for more information. If it’s deleted, it’s probably sold already.

Today’s selection has several interesting Infinity speakers, Speakerlab 7s, and several others worth checking out!

Bose Pair of 501 Series II Direct Reflecting Speakers – $180 in Renton

BOSE pair of 501 Series II SPEAKERS

These look like they’re in pretty good shape for their age. Basically half of a Bose 601 speaker, these have a front-firing woofer and pair of angled rear-firing tweeters to produce that wide, direct/reflecting sound vintage Bose systems were known for. They’re known to be sensitive to room placement, but when set up properly are a great small floor speaker system.

Dahlquist DQ-10 – $400 in Seattle

Dahlquist DQ-10

Wide and hefty, these vintage Dahlquist speakers have a very interesting time aligned driver array and crossover network designed to maximize sonic accuracy. They’re nearly 4″ wide and weigh 62 lbs. each, delivering a flat frequency respnose 37 Hz – 27 KHz. Freshly re-foamed, too, so they should be good for a while!

Infinity Modulus Speakers – $350 in Woodinville

Infinity Modulus Speakers

These Infinity speakers are in a beautiful piano black finish and feature a 5.5″ woofer and EMIT-K tweeter in a non-resonant cabinet. The EMIT-K goes all the way to 45 khz, almost double the range of human hearing, so if your favorite music benefits from the presence of ultrasonic harmonics, these might be the speakers to get. They’d likely work well as near-field monitors, too, with the fantastically accurate planar tweeter.

Infinity Reference RS 625 Speakers – $190 in Poulsbo

Infinity Reference Standard Speakers!

These feature Polycell dome tweeters instead of EMIT planar tweeters, but would still make a fantastic surround sound system for your home theater. Quintessential 90’s look to them would match many decors, too – and a decent price!

Infinity RS 5000 – $100 in Monroe

Infinity Speakers RS 5000

From the late ’80s, these Infinity RS 5000 speakers feature a 10″ woofer and 2.5″ mi-range, both made of semi-transparent polypropylene for exceptional cone stiffness, and an EMIT-K tweeter up top. With response from 42 Hz – 45 KHz, I’d love to have a pair of these as bookshelf speakers in my office.

Legacy Audio Signature III Speakers – $1800 in Bothell

Legacy audio Signature lll

Fantastically high-end audiophile speakers, these each feature 3 x 10″ woofers, dual 7″ mid-bass drivers, a 1.25″ dome midrange, and a 4″ electrostatic ribbon driver, flat from 20 Hz – 30 kHz. With that response, and weighing in at 130 lbs. each, you wouldn’t need a subwoofer with these! Beautiful natural wood grain finish, too. I’d love to hear how these sound.

Realistic Mach One Speakers – $175 in Seattle

Mach One Radio Shack Speakers

From back when Radio Shack produced something worthwhile, these Realistic Mach One speakers are collectible and well regarded today. With a 15″ woofer, multicell exponential horn midrange and horn tweeter these speakers have a fantastic presence in the room and will reproduce 25 Hz – 20 KHz. The grilles cover the lower cabinet but leave the top multicell horn exposed, making a very interesting presence in the room. These were freshly re-foamed and re-coned, so should sound great and last for a long time.

“Set of Two Stereo Speakers” – $39 in Bellevue

set of two stereo speakers

These look like they could use some TLC, but are intriguing. The multicell horn reminds me of the Pioneer CS series from the ’60s and ’70s, and I don’t recognize anything else. They could be Pioneers which have seen better days. Might be an interesting project?

Speakerlab 7s – $499 in Tacoma

Speakerlab 7

The Speakerlab 7s were made right here in Seattle, and feature a large and highly efficient 12″ woofer, 10″ passive radiator, and use Electro-Voice drivers for the mid-range and treble horns. The vertical midrange horn will produce a fairly narrow sound field, but otherwise, these are known as thumping hard and delivering exceptional clarity. Truly a fantastic rock speaker from the classic hi-fi era.

If you’re in the market for some new speakers, please click through to the sale ads and contact the sellers! Good luck!

Other Issues of the Speaker Spotter

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1946 Zenith 6-D-029 Consoltone Antique Radio Repair

Posted on April 7, 2014 by retrovoltage

This was a very interesting Zenith tabletop radio from just after WW2, the 1946 Zenith 6-D-029 Consoltone mantle radio. This is one of the iconic “boomerang” dials Zenith produced for a couple of years after the war. A variety of sets were made with similar styling; in this case the 6-D-029 is a 6-tube AC/DC radio with a combination of octals and loctal tubes.

This radio was repaired in the ’90s by a radio shop in Portland, OR but came to me in non-working condition. That’s not unreasonable for a radio to need another round of service after 20 years, and it looks like they did good work last time.

Checking out the tubes, other than one which was conveniently labeled (and testing confirmed) “weak”, they all had good filaments and good emissions. Something else was clearly the problem. Given the set’s owners don’t own a tube tester, the tube labeled “weak” must have been from the last time the radio was serviced; this one was the RF amplifier front-end tube.

It’s been pretty well cared for – the cabinet is in solid shape and there’s only a tiny amount of dust inside. Underneath, however…

There are several things going on here. Number one is somewhat obvious: something has released some smoke inside. In addition to that, the electrolytics used in this repair were different ages. There’s the blue CDE dual-section capacitor, and a Jamicon 33uF 450V capacitor hooked up as the second filter. Time to start pulling parts.

That Jamicon capacitor is visibly bulging from one side, and testing confirms it’s definitely dead. Of the CDE dual cap, one section was badly out of spec, and the other section tested open as well.

One of the ceramic disc capacitors blew itself apart – rather violently damaging a mylar capacitor near-by and generally making a mess of things. I replaced all of the same model of capacitor with new 630V film capacitors just to be safe.

After replacing the components it was time for the first power-up. No smoke! But, no sound either. Checking around on the voltages, something wasn’t quite right. B+ on the output tube was about 50% high, and there was no voltage on the screens of any tube.

Careful inspection and wire tracing got to the root of the problem: the wire between two tie points, supplying high voltage to the screens of the output tubes and the plate and screens of the RF and IF tubes, had broken at some point – likely from 68 years of metal fatigue. This was likely the root cause of the original failure: the ceramic disc capacitors were rated at 100V. With 4/6 tubes not conducting, the power supply was delivering over 160V when the nominal operating B+ was about 100V under load. This is well over the rating of those ceramic capacitors and could have caused the violent failure which took the radio out of service.

That’s more like it! A jumper confirms the issues has been located. The new capacitors are rated 630V, so should have no trouble with voltage spikes.

I soldered a 2″ segment of wire to make the connection permanently.

With that repair made, the radio fired up loud and clear!

Time to adjust the alignment a bit:

Then finally, back into the cabinet and ready to go home.

With all new film and electrolytic capacitors, and a replacement tube, this Zenith table radio is going to last a very long time before it needs to be serviced again and sound great the whole time.

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The Speaker Spotter – Speakers of Craigslist – April 4th, 2014

Posted on April 4, 2014 by retrovoltage

There’s always something interesting for sale on Craigslist, especially in Seattle. Do click the titles to see the original postings with more photos and additional information if you’re interested – otherwise, enjoy the virtual window shopping! Rain City Audio is not affiliated with any of these sales; contact the respective sellers for more information. If it’s deleted, it’s probably sold already.

Today we’re featuring some speakers which are rare and nothing short of exotic – very interesting stuff!

Greybeard Audio KB22 Speakers – $800 in Renton 

Audiophile Greybeard Audio KB22 Speakers 2 Audiophile Greybeard Audio KB22 Speakers 3

Weighing in at an astonishing 115 lbs. each and with an interesting tiled case, these Greybeard Audio speakers feature a 7″ woofer and 1″ dome tweeter and handle up to 300W at 6 ohms. At that weight, these must really have next to no resonance. I’d love to hear how these sound! I know these actually sold just a little while ago, but they’re so unique they deserved including anyway.

Duntech Soverign 2001s – $6500 in Poulsbo

DUNTECH SOVEREIGN 2001

These astonishingly massive speakers are reportedly regarded as some of the most accurate loudspeakers in the world, with 7 drivers in a time-aligned arrangement stacked vertically and weighing in at 325 lbs. each. With such a commanding presence, these make a serious statement.

Empire Royal Grenadiers Speakers with Marble Tops – $800 in Edmonds

Empire Royal Grenadiers Speakers with marble tops Empire Royal Grenadiers Speakers with marble tops 2

These are a rare collector’s item from the 1960s and feature large cylindrical cabinets with marble tabletops. In addition to the visible drivers, there’s a 15″ downward-firing woofer in the bottom. The only trouble is, if these speakers sit without being used for many years, the woofer cone can sag out of alignment with the magnetic field and and cause poor performance. Reportedly, it can be fixed by reversing the polarity on the woofer, turning it upside down, and playing it for a while to shake the cone back into alignment although there are mixed reports of success with this approach. As long as the speakers are continually used they won’t suffer this issue but sitting for many years can cause the sag. The seller reports they don’t have a way to test them; as a part of an estate sale, I’d expect the woofer is probably suffering from sag and will need to be adjusted or replaced.

Pair of Modular Component Systems MCS 8320 Linear Phase Speakers – $65 on Vashon Island

Pair of Modular Component Systems MCS 8320 linear phase speakers

MCS was the JC Penny house brand, but in the ’70s even house brand speakers could be pretty decent. These 3-way MCS speakers feature time-corrected driver alignment.

Pair of Wharfedale PPX-1 Speakers – $60 in Northgate

Pair of Wharfedale PPX-1

These are a bit of a mystery. The seller doesn’t have much info other than they take 70W at 8 Ohms, and are 22″ x 20″ flat speakers. Are these electrostatic panels? Or a proprietary short depth speaker? Difficult to tell the date, too.

Petroff Labs Reference 3-way Speakers – $550 in Bremerton

Petroff Labs Reference 3 way speakers

Featuring 12″ woofers, 6″ midrange and a 2″ ribbon tweeter, I’m sure these interesting trapezoidal oak speakers sound as good as they look!

Polk RTIA9 Tower Speakers – $1100 in Issaquah

Polk speakers rtia9

These beastly tower speakers by Polk Audio have an interesting driver compliment – three 7″ woofers, two 5.25″ midrange drivers in their own tuned internal enclosure and a 1″ dome tweeter, these speakers are flat from 30-26,000 Hz and accept up to 500W of input power. These would be great front channels for a powerful home theatre system!

Vintage JBL C35 James B. Lansing Speakers – $1800 in Burien

Vintage JBL c35 James B. Lansing Speakers

These JBLs look to be from the late ’60s, possibly early ’70s, and seem to have a large single full-range driver installed in the cabinet. JBL’s vintage speakers are all known to be pretty fantastic and I assume these are no different.

Vintage Kenwood KL-8080X Speakers – $500 in Bremerton

Vintage Kenwood kl-8080x Speakers

These mammoth late ’70s, possibly early ’80s Kenwood speakers, feature a 5-way design in a ported enclosure with a 15″ woofer, 6″ mid, tweeter, super-tweeter, and horn with level adjustments. I’m very curious how these sound – Kenwood’s vintage products tended to be pretty well designed but I’m not familiar with these ones specifically. I do think the price is a bit high, but these have been up on Craigslist for months, the seller might be a little flexible now.

Like what you see? Check out more back issues of the Speaker Spotter.

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1940 Philco 40-185XF Antique Radio Restoration

Posted on April 2, 2014 by retrovoltage

I had the privilege of working on a very well preserved Philco 40-185XF recently. These are top performing pre-war sets featuring 8 tubes, an RF amplifier front-end and push-pull audio output into a 12″ speaker. Definitely worth fixing up! This radio had been its owner’s family for years – first in his grandparent’s home, then with his parents, before it passed on to him. After serving as a conversation piece for many years, it was time to get it going again.

This model had been sitting silently since the 1970s and was ready to come back to life. It came to me for a complete overhaul, including testing all the tubes to replace as needed, re-stringing the dial, replacing hardened rubber mounts and eroded pushbuttons, and a precision alignment.

The underside is nicely laid out and pretty easy to work on. There’s a few capacitors which are buried, but most are easily accessible. The output transformer, top left, is mounted under the chassis instead of on the speaker as was more common on earlier sets.

Component replacement was initially pretty straightforward. The preset assembly was held in by two screws and had plenty of slack to fold it up and out of the way to allow easy access to the components beneath it. There were several small capacitors and an electrolytic can mounted under the pushbutton assembly.

The power cord was in dire need of replacement, so it received a new polarized plug and new X1Y2-rated safety capacitors on a newly mounted terminal strip.

With component replacement complete, it was time for a first power-up and a test signal. All seemed to be good at first for a bit…but then the radio sputtered a bit and cut out entirely – then some faint smoke started to appear! Bad, bad sign. I killed the power quickly to avoid damaging anything and carefully inspected the fault.

On this schematic snip, the resistor circled in red was the one which was overheating and smoking. This resistor feeds the high voltage to the front-end of the radio; overheating means excess current drawn. I pulled those tubes, but it continued to smoke, so further investigation was necessary. First, I replaced that resistor with a new one which hadn’t been heat-damaged.

It’s a bit faint, but the insulation had cracked off the wires leading into the IF can and were shorting to the chassis. That’d be the problem! Time to pull the IF can:

Some wires were cloth and some rubber-coated; some of the rubber coated ones were fine, and some were brittle and cracking. I sleeved the damaged wires, then reinstalled the transformer in the can and mounted it back up. One problem solved! The short circuit was fixed, but there was still no audio output – even when injecting directly into the audio amplifier circuit.

There were some clicks when I’d touch certain resistors with a probe. The resistors had overwhelmingly tested within tolerance so most were left original, but something happened along the way. I pulled the suspect resistors to replace, and examined the old one:

It’s tough to see – but the body of the resistor is cracked! This was a new problem. What happened is: carbon composition resistors absorb moisture from the atmosphere over time. In this case, the radio is 74 years old, and 44 of those years it sat without being played. Resistors also dissipate heat when they’re operating. This combination caused the absorbed moisture to expand and escape by cracking the body of the resistor and causing intermittent opens. Not good for performance! I replaced nearly all the remaining resistors at this point.

The replacements are 1% tolerance precision metal film resistors which should last for a very long time, and don’t absorb moisture the way carbon resistors do. Now, I was able to get audio, but no radio reception. Testing the front-end verified the radio was operating, but it wasn’t tuning a signal. Time to investigate the band switch – which, surprise, was badly gunked up! The mechanism wasn’t allowing the tuning capacitor to engage, and all the contacts were badly corroded which was killing the signal.

You can see how much gunk and oxidation had caked up onto the switch contacts – on the left, not processed; on the right, cleaned and scrubbed.

With that, the radio roared to life and picked up stations loud and clear across the dial! There were a lot of problems, but they were all able to be corrected. I peaked up the alignment using my standard signal generator, then did final inspection checks.

Finally, it was ready for the trip home! It sounded even better installed back in the cabinet.

The owners had the cabinet refinished while the radio was in the shop – it’s a perfect pairing! New pushbuttons and new rubber mounts and the radio is nearly as nice as they day it left the showroom floor.

This family heirloom is back in running shape and is going to serve faithfully for many years to come as a beautiful piece of functional furniture. Just look at it!

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1938 Zenith 5-S-220 eBay Tune-Up Special

Posted on March 26, 2014 by retrovoltage

I’ve had the opportunity to work on several very nice Zenith radios lately and this one is especially interesting. It’s the Zenith 5-S-220 Cube. This is the first time I’ve seen one of these in person, they’re somewhat uncommon. Electrically, it’s a nice 5-tube radio with a broadcast and shortwave band, and the cabinet is very compact with the speaker firing vertically through the top of the cabinet. The black dial in the face is very easy to fine-tune.

It was sold as in running condition, and it worked okay on the standard broadcast setting, but with the switch on the Treble Cut tone setting the set picked up bad warbling low-frequency interference, called motor-boating. It also just didn’t sound that good, and Zenith radios are known for their excellent tone even from their small radios.

The chassis is supported on small risers to replace compressed paper spacers. It’s fairly cramped in there,but the chassis slides out easily when the spacers are pulled out and the speaker socket makes service easy.

Underneath, the solder joints were all very good in fact. Mostly original resistors retained.I tested the resistors and many were well outside of their specifications; there were several other problems as well.

The previous service had replaced all but one of the original vintage tubular capacitors that are candidates for replacement in any vintage radio.

The resistors were all original. This frequently isn’t a problem – vintage resistors can still test within tolerance, and if so, don’t need to be replaced – but these were almost all bad. I found some which measured as much as 250% of their marked values. The radio actually played like this, it just goes to show you how robust these tube circuits were. They’d tolerate a lot of abuse and still sound passable.

I replaced the vintage capacitor and many resistors but the motor-boating persisted. Throughout all of this, the volume is lower than I’d expect, too. I went about replacing the Micamold capacitors which can frequently go leaky and exhibit odd symptoms. These are in fact paper capacitors in a molded package – not true mica capacitors which tend to hold up well even today.

While poking around at those connections, an entire solder blob moved – the ground connection had broken off entirely:

I replaced this one with a true mica capacitor and a solid ground connection. A few tweaks to the alignment later, the motor boating was gone, but the low volume persisted. Even on the normal position it was still lower than it should have been. I examined the tube line-up versus the schematic. This radio had a 6V6GT tube installed when the radio was designed for a 6F6G tube.

In general, those tubes are “fairly” close and you can often plug them into each other’s sockets. The radio will play, but with more distortion and lower volume, as they do have distinct design characteristics. The mismatch will get you significantly lower volume as a result, too. I had a 6F6G which tested like new in stock and made the exchange:

With this, the radio roared to life with perfect volume. It sounds absolutely fantastic, especially for such a small cabinet and speaker. It also goes to show: be cautious buying radios on eBay. They might even work, but often may have hidden problems like this. It’s worth it to ask for under-chassis photos to check the amount of work that was done.

With the feedback problem corrected, I performed a precision alignment and the dial tracks in perfectly.

Overall, to bring this radio up to standard I replaced many resistors, replaced several capacitors with modern technologies, repaired a broken ground connection for the capacitors, aligned the radio using a standard signal generator,  and replaced a wrong tube. Now it looks as good as it sounds – practically brand new.

Posted in Electronics, Projects, Radios and Tubes, Vintage | Tagged , , , , , , , , , , , , , , , , , , , , | Leave a comment

The Speaker Spotter – Speakers of Craigslist – March 21st, 2014

Posted on March 21, 2014 by retrovoltage

There’s always something interesting for sale on Craigslist, especially in Seattle. Here’s a selection of especially notable vintage speakers and other audio products for sale on the local Craigslist. I’m not affiliated with any of these sales, but if you’re interested, you should contact the seller through the respective Craigslist page! Do click through each of the titles – the original postings contain a lot more information and many more photos, along with the seller’s contact information to request more information. If the ads are removed, the speaker probably sold, so don’t be alarmed if some links don’t work. Try searching for the keywords as sometimes they expire or are reposted.

Today we have several unusual boutique hi-fi speakers, plenty of vintage JBLs, and an interesting set of Klipsch La Scalas designed for stage use.

Cerwin Vega Speakers – $125 in Olympia

Cerwin Vega Speakers

Cerwin Vega speakers are known as great rock speakers that can handle a ton of power and pump out a lot of bass. I’ve owned a pair and they are great performing, general use speakers. The iconic red foam surround and solid wood grain are very attractive and eye-catching, too.

DCM TimeWindow 1A Speakers – $200 in Ballard

DCM TimeWindow 1A

I understand DCM Time speakers to be nice and accurate, if a bit understated, but I’ve not heard them myself. Based on the cabinet design I expect these might be bipolar speakers? Looks worth investigating!

JBL 4330 Custom Studio Monitors – $3000 in Eguene, OR

JBL 4330 Custom Studio Monitors

If you’re into music production, or just like an extremely accurate listening experience, these might be for you. They feature the iconic biradial “butt cheeks” horn and what looks like it could be a 15″ woofer. I’m sure this is both powerful and great sounding.

JBL LE-8 Vintage Speakers – $299 in the Renton Highlands

JBL LE-8 Speakers 1

JBL LE-8 Speakers 2

A throwback from the modern reference quality JBL above, these are very vintage JBL bookshelf speakers with a single full-range driver installed. I’m sure they’d sound very warm with a matching vintage tube amp or low powered transistor amp up to a couple dozen watts, but might not have the same clarity and definition you’d get with a slightly newer, multi-driver speaker system.

Klipsch La Scala LSI – $1500 in North Bend

Klipsch Lascala LSI 1

Klipsch Lascala LSI 2

The Klipsch La Scala is another of their high-end folded horn speakers; these are the LSI variant which are designed to be stage speakers with detachable treble horn cabinets. The seller claims these were never hauled around to gigs, though, and are in great shape. The same great sound from a Klipsch folded horn, but in a bit more industrial of a package.

Revox AX5-4 Speakers – $295 on Seattle’s Eastside

Revox AX5-4

Revox AX5-4 2

From 1977, I’m not familiar with this brand, but they’re reportedly using high-end German manufactured drivers; a 3-way design with dual woofers can probably offer plenty of bass. The mid driver resembles the Infinity polymer dome, too. Rated for 100 W power handling at 4 Ohms, 91 dB efficiency these seem like they’d be worth checking out. I’d love to listen.

Snell C IV Speakers – $399 in the Renton Highlands

Snell C IV Speakers

These Canadian hi-fi speakers have some interesting engineering in them, including a zero diffraction grill which is designed to be more sonicly transparent, and an interesting dual tweeter design with a front-firing tweeter on a fourth-order crossover, and a rear-firing dome tweeter on a first-order crossover. This combination apparently delivers great accuracy from the front while the rear – which can be disabled – fills out the volume lost due to the steep crossover slope.

Totem ARRO Speakers – $800 in Auburn

Totem ARRO Speakers

These no-frills 2-way audiophile speakers look like as much of a decor statement as a music piece. They’re “wife friendly” and yet regarded for excellent bass response and well defined imaging. I’m not sure it would match every decor but it’s very pretty.

Universal CX-300 Hi-Fi Speakers – $140 in Everett

Universal CX-300 Hi-Fi Speakers

Universal CX-300 Hi-Fi Speakers 2

These early ’60s drivers throw back to the coaxial design which was more common at the time. With 25W of power handling and meeting the DIN Hi-Fi spec of 40-18,000 Hz frequency response I bet these sound great with a period tube amp like they would’ve used originally.

Vintage JBL L88 Nova Loudspeakers – $400 in Tacoma

Vintage JBL L88 Nova Loudspeakers

Vintage JBL L88 Nova Loudspeakers 2

These are beautiful speakers which look to be from about the early ’70s. I’m sure they sound fantastic like most JBLs, especially vintage JBLs, and would make a perfect vintage hi-fi bookshelf or desktop system that would look great in almost any room.

More Speaker Spotter

Posted in Audio, Collections, Photos, Speakers, Stereo, Vintage | Tagged , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , | 1 Comment