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Old 10th February 2013, 09:34 PM   #1
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Question DuMont Stereo Tube Console late 50's - What to do?

Hello everybody.

I am new here, by profession I am electronics engineer, but never worked with tubes as professional, although audio (up to now - discrete and IC only) has always been my passion

I recently bought from Craiglist old DuMont Stereo Console, late 50's, solid wood, all-tube design. ALL WORKS, just usual scratch on pots.
My initial intention was to use it as a separate AM/FM/Receiver or even just as small tube amp. So I opened the box and started investigating what I've bought, made some photos and have discovered the complete paperwork inside (no exact date of manufacturing, though), including schematic.
The fact I've discovered so far about it:
1. The Console as a whole is in outstanding cosmetic condition - just few scratches on the corners, but otherwise looks like new - old lady I bought it from was first and the only owner. The original labels says:
DUMONT TELEVISIONS & RADIO Montreal, Canada, Model DS-136. Google gave me nothing on that...
2. The turntable is BSR (Birmingham Sound Reproducers) Made in Great Britain - pretty ubiquitous old timer brand for low-end turntables. It's automatic, with ceramic cartridge which sounds terrible in the condition it is now. Cartridge is BSR N-50, needle type - 133 - absolutely NO INFO about the replacement of these...
3. Radio/Amp works and sounds amazing for the age. I am attaching the schematic, among with photos. The amp (the part I am most interested in) is based on 12AX7 pre-amp and dual 50EH5 power amp (datasheet shows 1.4W output power per channel). The sound of the radio is AMAZING - dead-lock on every station and even AM sounds like FM in modern radios!
4. Speakers are one 8" woofer and two 2" tweeters, Made in Japan. Again - condition is like new, no tin sound, no rattling or clanking.

Well - that is about the system I've got, described in short. The million dollar question is:
"What is the best to do with it?"

I see the following options:
1. To restore (recap, clean and refurbish as much as I can keep to original) the WHOLE BOX. I am very hand and have restored electronic items all my life, so that's not a problem. The problem is that the unit is too big to keep it as an original stereo in a room. Any idea how much unit like this in mint condition with all original papers may cost retail?
2. To get the Receiver Module out and put it in a nice stainless/aluminum/plexi box with all in/outs connectors, etc. Any idea will that worth the effort? Again - making a nice boxes is my passion, so I don't mind the extra work, the question is will the amp worth it?
3. To keep the pre-amp/amp only and make a complete new case, as described in #2.

What according to you would be the best choice for me?

I am completely open to any suggestions and will not feel offended from straight, but honest professional opinions, so feel free to advise!

Thanks sin advance, guys!
Attached Images
File Type: jpg DuMont Console - Top.jpg (644.8 KB, 339 views)
File Type: jpg DuMont Console - Middle Section.jpg (644.3 KB, 323 views)
File Type: jpg DuMont Console - Receiver.jpg (699.7 KB, 313 views)
File Type: jpg DuMont Console - Speaker.jpg (671.2 KB, 308 views)
File Type: jpg Schematic.jpg (672.0 KB, 325 views)
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Old 10th February 2013, 10:07 PM   #2
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I've disassembled a couple of these, Having the schema is nice, thanx.

At some point a pr of 50EH5 monobloks.

The 8" is an RSC. If you are lucky they are the ones with isophon comes. Even the others are quite reasonable.

The turntable is of little utility.

dave
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Old 10th February 2013, 10:17 PM   #3
pdul is offline pdul  Denmark
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Recap it and shine it up with teakoil, it would be a sin to kill a jewel like that, and even if its dificult to get a new ceramic pu. it is not impossiple.
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Old 10th February 2013, 10:29 PM   #4
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You already seem to be clued into the fact that the BSR TT is a POS. It should not be allowed near precious LPs. Piezoelectric cartridges can literally scrub the HF info. out of record grooves. Also, high tracking forces induce general wear.

The circuitry is quite interesting; series heater strings, but strictly AC operation. While it's low power, it's not especially cheap. Notice the tertiary, local cathode, NFB windings on the O/P transformers. That cost some money.

Eliminating C68, C69, and R50 is a must do. Along with that, install a proper, 3 wire/safety grounded, power cord.

Replacing all electrolytic caps. in "vintage" units is a matter of routine.

I would rework the 1/2 wave rectified B+ PSU into a full wave bridge using 4X UF4007s, but you have to pay very careful attention to the grounding caps. in the tube heater setup. Install parts of a vastly higher working voltage.

Replacing any of the RF/IF tubes will require realignment.

The Russian 6H2Π (6n2p) is not a plug in substitute for the 12AX7/ECC83.

Trying some borrowed HIGH efficiency horn speakers with the Dumont electronics is (IMO) worth a shot.
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Last edited by Eli Duttman; 10th February 2013 at 10:38 PM. Reason: fixed typo
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Old 10th February 2013, 10:44 PM   #5
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You can use 6Н2П tube instead of 12AX7, but powering it's filament from 6.3V supplied for pilot lamps, and replacing 12AX7 filaments by resistor, to provide 12V voltage drop on it.
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Old 10th February 2013, 11:43 PM   #6
kevinkr is offline kevinkr  United States
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Note the fact that it has a stereo multiplex decoder built into the FM tuner dates the console to sometime after April 1961 as the Canadian FM stereo broadcast standard approval of the Zenith/GE system by the DOC presumably followed the U.S fairly quickly.
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Old 11th February 2013, 12:18 AM   #7
Magz is offline Magz  United States
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I rescued an old Grundig NF1 amp from a Grundig Majestic console (8.5wpc, ELL80) and made it into an i-pod dock for my wife - maybe that's an idea for ya. It even charges the ipod; the copper top has acquired a nice patina over the last year since I built it.

See pictures.
Attached Images
File Type: jpg Grundig Majestic Console Amp.jpg (94.3 KB, 196 views)
File Type: jpg ipod dock2.jpg (27.9 KB, 117 views)
File Type: jpg ipod dock.jpg (25.2 KB, 113 views)
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Old 11th February 2013, 12:22 AM   #8
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Thank you very much for the advices, whoa, that was fast, amazing forum! I really, really appreciate the help!

I still have a lot of homework to do (cleaning is already done and I have removed the main unit from the wooden box) - learning and start making improvements without (for now) altering the original functionality.

I must assure you, though, that at least for a while I will keep everything "backward compatible" - e.g. I can always put everything back.

I'll start with recaping and new power cord.

Quick questions:
1. Eli Duttman, should I replace or remove R50 and C68, C69. At my understanding it's nice to have AC filer, no?
2. Changing the rectifier to full wave is very good idea, but this would increase the effective DC voltage, right? Will that change the bias?
3. What do you mean exactly by "HIGH efficiency horn speakers" - speakers with mechanical design allowing high acoustic output? Can you give me a link?
4. Are there a chances to use at least ceramic cartridge with that unit?

Did anybody do that with old BSR TT?

Wavebourn, thank you for the clarification, I knew that some mods were needed, thanks for details.

kevinkr, thanks for the note - I assume that will consider the console to be "Early 60's", right? Clips on YouTube showed "Late 60's" Dumont consoles with solid-state already...

Once again - thanks everybody, keep going, I will post the updates too!

Cheers!
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Old 11th February 2013, 03:36 AM   #9
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Quote:
Originally Posted by Old Hush View Post
Thank you very much for the advices, whoa, that was fast, amazing forum! I really, really appreciate the help!

I still have a lot of homework to do (cleaning is already done and I have removed the main unit from the wooden box) - learning and start making improvements without (for now) altering the original functionality.

I must assure you, though, that at least for a while I will keep everything "backward compatible" - e.g. I can always put everything back.

I'll start with recaping and new power cord.

Quick questions:
1. Eli Duttman, should I replace or remove R50 and C68, C69. At my understanding it's nice to have AC filer, no?
2. Changing the rectifier to full wave is very good idea, but this would increase the effective DC voltage, right? Will that change the bias?
3. What do you mean exactly by "HIGH efficiency horn speakers" - speakers with mechanical design allowing high acoustic output? Can you give me a link?
4. Are there a chances to use at least ceramic cartridge with that unit?

Did anybody do that with old BSR TT?

Wavebourn, thank you for the clarification, I knew that some mods were needed, thanks for details.

kevinkr, thanks for the note - I assume that will consider the console to be "Early 60's", right? Clips on YouTube showed "Late 60's" Dumont consoles with solid-state already...

Once again - thanks everybody, keep going, I will post the updates too!

Cheers!
The Hedlund Horn is an example of what I mentioned. The "full range" driver used is by Lowther and, in some versions, can produce a SPL of over 100 dB. at a 1 M. distance, when driven by 1 W. That's the kind of speaker sensitivity needed to do serious listening with an amp like your Dumont and its "flea power". Google Lowther Medallion for another example.

Scan the archives for "Death Capacitor". Unfortunately, C68, C69, and R50 fall into that category. Please adhere to contemporary safety standards.

Please provide a close in photo of the BSR headshell and cartridge. There's an outside chance of being able to mount a low cost mag. cart. in place of the piezoelectric POS. Ceramic carts. are piezoelectric and to be avoided. Frankly, it's better to scrap the BSR TT and install a "vintage" Technics, Pioneer, or BIC TT intended from day 1 for use with mag. cartridges. Jim Hagerman's "Bugle" phono preamp is a quite decent, inexpensive, solution to the problem of interfacing a mag. cart. to the Dumont electronics.

Full wave rectification will not increase the nominal voltage of the B+ rail. Remember, a cap. I/P filter charges up to 21/2 X the AC RMS voltage and drifts downward, under load. Switching to full wave rectification doubles the ripple freq. (twice as many charging pulses) and increases the effectiveness of the PSU filter.
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Old 11th February 2013, 12:23 PM   #10
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Thanks a lot, ELI, I will check out the links and advises. Will have a lot of fun now.... ;-)
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