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Help me!!! I need schematic of Pow-Amp using 6V6

Hello all,

I am the new comer. Las tweek I got a 2nd-hand power amp in Ebay. Tube compliment is one 5Z3 rectifier, one 6N7, one 6C5, and two 6V6G outputs. The problem is it has no input and speaker connectors. I've been looking for schematic for the pow-amp using 6V6 but I could not find it.

So I need your help. If you have or know that, plz send it to me or let me know the link.

many thanks in advance!!!
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
> it's lost all the connectors but I have tested the OPT and Power Trans, they are OK

Then you must have some loose wires where the connectors used to be.

The input goes to the 6N7 Grid, with a resistor or two, maybe a capacitor and potentiometer as well. You can recreate this by looking at nearly any tube-amp plan.

The output transformer has several leads to go to the speaker connector. Note the COLORS! There was some semi-standardization, which will speed identification. For example, a Black lead is most-likely the Common of all the speaker windings, and probably grounded (unless it has variable damping).

Are there any markings left to indicate the impedance(s) it supports? While you can derive these by measuring voltage-ratios (assume a P-P 6V6 primary is 10K), if you know the impedances you can guess the wires by their DC resistance (use an old fachioned analog ohmmeter; digital meters are sometimes confused by transformer inductance). Or you can run 8Ω on a 4Ω or 16Ω winding, the 6V6 is not too fussy; but it could have 25V or 70V windings which will be quite unhappy with 8Ω loads. (My 1939 PA amp has only 3.2Ω and 70Ω {500Ω} windings.)
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
Thanks for schematic.

Yes, all the electrolytic caps are going to blow at power-on.

Actually, half of them won't blow until you plug-in the speaker field-coil. The 4-pin socket next to the power supply choke. Since the speaker is long-gone, put 2K 20 watts on the two pins that don't go to the output transformer. After all the caps have burnt-out and have been replaced, measure the 6V6 plate voltage (not over 300-350V) and the 6V6 current (measure the voltage and resistance on the negative end of the big bleeder resistor and do math) (80mA/pair is plenty for 6V6).

This is an antique. Note the grid transformer: old even for 1938. Note that the resistor values say "M" where today we would write "K" ("500M" is really 500,000).

OK, the input is odd. The radio section had separate "bass" and "treble" outputs, but no filters in the radio. 6N7 is a dual triode: bass/treble filtering is done in the two plate circuits. The simplest way to "get sound" is to disconnect everything on the 6C5 Grid except the "500M" resistor, and drive it with a line-level signal. That will work fine, though gain may be a mite low.

Otherwise cut the 0.05 and 0.004 caps out of the 6N7 plates, and drive the grid that makes sound: this will work one half of the 6N7 at full bandwidth.

No clue what speaker impedance is. I would assume 3.2Ω on the internal, and it may take another 8Ω load on the un-labeled winding (this is unlikely to be a 70V line). You can throw 8Ω speakers on the 3.2Ω tap, it will work fine.
 
Thank Tom and everybody in the 4rum.

The schematic is so nice. I think in the future all the Caps should be replace and the better sound will be achieved. But one thing I am wondering now is the value of the capacitor: 8MFD is 8 micro farad, that's right, isn't it?.

one more thing, I want to replace all the bulbs but plz let me know where and how can I buy them??

I'm waiting your suggestions.

Many thanks in adv.