Silvertone (Sears) stereo amp

[tubelab.com]

One HV lead from the power transformer goes to the junction of the two diodes. One diode goes to ground, the other goes to the floating capacitor. It looks like the other HV transformer wire goes to the negative side of the floating capacitor, and to the positive side of one section of the multisection capacitor. This is a classic full wave voltage doubler. There is probably no center tap.

[Eli Duttman]

Percy,

The presence of a single snubber cap., along with cathode to anode wiring of the diodes, confirms the PSU is a voltage doubler. Replace the OEM diodes with UF5408s. Replace the snubber cap. with a 10 nF. part rated no less than 1 KWVDC. A 2 KWVDC AVX brand part from Mouser is not at all expensive and you'll have peace of mind.

All electrolytic caps. must be replaced. LARGE value 'lytics in the doubler stack keep the rail voltage up and suppress the ripple fundamental, but they generate ripple overtones ("hash"). A choke between the doubler stack and the 2nd filter cap. suppresses the "hash." Available space may prevent the use of a "typical" PSU choke, but Mouser stock # 542-5900-103-RC (a 10 mH./250 mA. part) will fit and kill the higher order overtones.

Sorry about the "fat finger" error in resistor value. IMO, a safety load seems the most likely reason for those parts.

If the OEM signal topology is retained, the Carbon composition resistors have to be checked for drift outside of tolerance and all ceramic caps. in the signal path need replacement with film parts. Replacing grid leak resistors with metal film parts is a good idea, as noise will be reduced.

[tubelab.com]

IMO, a safety load seems the most likely reason for those parts.

Some of these consoles had headphone jacks (my fathers does). When the headphones were plugged in, the speakers were disconnected. Some also had external speaker connections and a switch to select which speakers were used. The possibility for no (or a high impedance) load exists.

[planet10]

Given the quality of the parts, you'll eventually want to replace all the passive parts... as Eli suggested, i would turn it into an El Cheapo variant...

(i had a similar amp -- can't recall what it was out of, probably a Viking or a Canadian-made Silvertone)

dave

[Smokehouse Bob]

I have this exact 6BQ5 amp. Does anyone have a schematic that would allow me to make use of these parts in a different amp? Maybe a small headphone amp?

[Smokehouse Bob]

Yoo Hoo, anyone have a schemo for this one?

[percy]

A gentleman on AA who had the same amp and did some modifications sent me a schematic. Its pretty straightforward. Let me ask him, if its ok with him I will send it to you.

although I probably will modify it to a SYRLD (SY's Red Light District).

[Smokehouse Bob]

Thanks Percy!!!! Hopefully he will be cool with it. Otherwise, I'll have to sell this one and I'd rather keep it and enjoy it.

[percy]

Ok here you go...
I believe the only "mod" from the original in this schematic is the triode switch.

Mind if I ask you where did you find it and how much it set you back by ?

[Smokehouse Bob]

Thanks Percy!! I gave 25 for the whole console. I still have the tuner, but I think the turntable is long gone. I was on my way to visit my mother-in-law in the hospital after hip replacement. I stopped by the thrifty and paid for it, coming back later to pick it up. Good Karma I guess, no? Thanks again to you and the kind gent over at AA!!