help with restoring amp

[skyraider]

Hi guys,

Im new to tubes. I just bought this jewel from an auction, and now im trying to repair it. Is anyone here familiar with this model? All i know, it is Japanese made, and i need more specs on it... Thank you!!

 

[skyraider]

another view:

 

[skyraider]

The back view:

 

[SY]

What a hoot! Are there any tubes under the chassis? I can only see one input tube on the top- surely this is a stereo amp? Solid state input stages maybe?

In any case, it will probably run about 15 watts per side.

 

[planet10]

What a hoot! Are there any tubes under the chassis? I can only see one input tube on the top- surely this is a stereo amp? Solid state input stages maybe?

I was counting the tubes too... my guess is that what we have is a 6BM8 PP amp with a twin triode as an additional pre-amp gain stage. 8W/channel. Honking big OPTs for 6BM8 thou.. maybe ECL86.

Skyraider, what tubes does it have?

And a photo of the underside.

dave

 

[SY]

Fooled me- I couldn't make out a second section in the output tubes and assumed 6BQ5 or something like that.

 

[planet10]

Fooled me- I couldn't make out a second section in the output tubes and assumed 6BQ5 or something like that.

I'm just guessing -- the Japanese do like the 6BM8.

I've just recently pulled a PP 6BM8 amp out of a console -- stripped it for everything but the 4 6BM8s -- one of the very few pulls i've got that works (it and an ELL80 stereo amp) -- those two amps bring the total to about 3%

dave

 

[Eli Duttman]

I agree that it's a stereo amp. Knowing the tube complement would help. Obviously, a schematic would help a lot. What has me wondering are the 6 controls, perhaps volume and tone for each channel. It would seem that there are not enough active devices on top to support the controls. Speculation about "sand" under the hood seems reasonable.

I'd like to see a close up of the label on the power trafo. I'd also like to see an image from underneath.

 

[planet10]

What has me wondering are the 6 controls, perhaps volume and tone for each channel. It would seem that there are not enough active devices on top to support the controls.

Volume, Bass, Treble x 2 makes sense... if the big tubes are triode/pentode, then the extra voltage stage in the 12AX7 (?) would give enuff drive for the tine controls ... no silicon required (except for rectification -- and there is a good chance it is currently a stack of selinium)

dave

 

[skyraider]

oh,
I have bought the thing but it has not been shipped yet, i will open it up only next week when it arrives..
The six controls baffles me to..... but i dont think its hybrid amp
anyway, whats sand and selenium??

thanks

 

[Eli Duttman]

whats sand and selenium??

Sand is tubehead talk for SS (Silicon).

Before Germanium and, later, Silicon based semiconductors came on stream, semiconductor rectifiers based on the metalloid Selenium were available. Selenium is in the same column of the Periodic Table as Oxygen and Sulfur. Selenium rectifiers look like a stack of square fins. Selenium rectifiers are accidents waiting to happen and MUST be replaced QUICKLY. It is only a question of when, not if, a Selenium rectifier will fail. When Selenium rectifiers fail, toxic vapor and dust is emitted. Other parts may be damaged too. You will probably have to allow for the smaller forward voltage drop modern Silicon diodes exhibit. The UF4007 is a good choice for fabricating Selenium rectifier replacements.