6l6 push pull output question(s)

[Bas van Dijk]

Yes, all within 0.5% the same.

 

[rayma]

pin 4 is at 310 V
Pin 3 at 410 (higher than in the schematic)
Pin 8 at 22V

Maybe the distortion is from the first or second stages of the circuit.
Try cleaning the tone switch. Replace the first stage cathode bypass capacitor.

 

[Alllensoncanon]

Also can you by-pass the tone stack and see if the problem are there. ie: Feed input directly to pin 1 of 2nd 6SN7.

 

[sser2]

Maybe the speaker is broken?

Check speaker's field coil continuity and resistance - should be about 6K.

Check for good contacts in connectors and rotary switches.

Check volume control potentiometer.

 

[Bas van Dijk]

I will check the switches, thanks.
All caps, resistors and tubes are new, amp is completely rebuild.

@Allensoncanon, are you saying the first stage is just tone stack and does not provide amplification? Good idea, I will check that.

Thanks guys, great forum! Appreciate all the quick replies!

 

[Alllensoncanon]

Bypassing tone stage is just to diagnose where the problems are. If distortion/low volume are gone, the problem are likely at the switch contacts and/or the ceramic caps that were soldered on to them.

Personally for old amp, I like keeping the tone controls to preserve the old sounds. However, if you want modern Hi-Fi sound or use it as your main amp afterward, I would remove the first stage and the tone stack. It should have enough gain for iphone/ehco type line devices. How about adding an extra set of RCA input which by-pass the tone stack.

 

[Bas van Dijk]

I found it!!

I feel deeply ashamed.. In rebuilding the amp I forgot to connect the anode pin of the first triode after the tone stack to the input pin of the phase inverter!!
I thought I checked the voltage on pin 4 but apparently did not and just assumed it was the same as pin 2... (assumption is the mother of all **** ups)

Connecting them increased the volume a lot and improved the sound quality and reduced the hum...

Pfff. Very happy. Amazing that the amp still produced reasonable sound without the connection...

Thanks for all the help!

BW,
Bas