TELEFUNKEN console stereo what do I need to know

[judge74]

Yesterday I bought a 1950s TELEFUNKEN Bayreuth II console stereo off of Facebook marketplace. I have been wanting a really nice MCM console for years and kept not finding a good deal until now. It has all of its original TELEFUNKEN tubes and looks to be really clean and complete. I have not tried to power it on.

I have fixed guitar amps off and on for years, I am not the best tech but I get by and always end up finding the problem. However, I have never worked on something like this. I found the schematic and looked at it for awhile. The amplifier portion makes sense, it is a single ecc83 running a phono preamp on a separate board by the turntable. Then there are 2 ecc83s into 2 single ended el84 power amps. Then there are 4 5x7 speakers and a 10 inch woofer. There is a some sort of crossover with 2 caps and 2 inductors. Even though it probably only makes less than 10 watts everything I have heard about it says it is plenty loud and full sounding.

It also came with an extra little stereo amplifier (model s81) that has 1 ecc83 and 2 el84s. I assume it was meant to run auxiliary speakers.

but I really don’t know anything about RF tuners. What do I need to know about working on a console that is different than a guitar amp? Is there anything that TELEFUNKEN does that is odd and different? What pitfalls should I avoid? Are there any good resources out there for these?

My plan so far is to open it up and look for anything obviously wrong. Burnt parts loose wires leaking caps etc. Be sure everything is plugged in the right place. Then turn it on with a light bulb limiter and a variac and hope for the best. I am thinking that I will probably need to replace all the e-caps and paper oil caps before I am done. I am really hoping I don’t have to mess with the tuner

I will post some photos and schematics but here are links to the documentation

https://www.radiomuseum.org/r/telefunken_bayreuth_ii_2.html

http://www.tube-classics.de/TC/GermanTubeHifi/Integamps/Telefunken%20S81/S81.htm

[Rontone]

I have picked up a few Telefunken radios before,

One that I did take apart to use some parts and the tubes, had RDE caps, which measured great and I'm still using some of them, probably bring it up really slowly, follow the tips on the tube-classics website, see if its good for hi-fi use as he says,

You could try the Telefunken tubes in your guitar amp while the radio console is 'reforming'

[judge74]

So the general plan would be to pull all the tubes so the filaments aren’t hurt by low voltage. Then since it is solid state rectified it will still make DC even at really low voltages. I could plug into the variac and start really low like maybe 20 volts and go up 10 volts every few hours?

[sluckey]

Tubes will not be injured by low heater voltage.

[judge74]

Tubes will not be injured by low heater voltage.

I have read a bunch of times on forums that low heater voltage is hard on tubes… are people just wrong about that?

[HotBluePlates]

Tubes will not be injured by low heater voltage.

I have read a bunch of timers on forums that low heater voltage is hard on tubes… are people just wrong about that?

If "low voltage" was the way the amp was always run, every day for years, then yes it would be hard on the tubes.  Mainly because the cathode might not be heated enough to fully activate the cathode coating, leading to interface resistance and early emission drop-off (translates to "shorter tube life").

But if you're just reforming caps, the tubes will not be at too-low-voltage for long enough to matter.  Kinda like driving 1 block on a flat tire vs going 30 miles.

[PRR]

The RF tuner may need a tube. Beginners should NOT try to "go through and freshen up". The exact layout is critical. In FM, a part-mm shift of part position may require full realignment to get useful performance. The tubes are run hard for OK performance at 100MHz but the other parts typically loaf.

High plate power at low heater voltage may strip cathodes. You will have low plate power by running low line and no signal. And as said, not for very long.