clean channel distorting. help please

[scotto]

71 Bandmaster with distortion in left channel. Changed all tubes with no difference. Where do I look next? Right channel is fine.

[Firestorm]

The Normal channel? Probably a bad resistor. The 100Ks off the plates on V1. Maybe the 1K5.

[pdf64]

Yes, may even just be a broken wire or dry joint; checking the Vdc of V1 and then comparing them to the Vdc on the same pins of V2 may help.

[Stevem]

My money's on those 100K resistors, what do you read for voltage on pin 3 and 8 of that first tube?

The cathode by pass cap off of those two pins may be bad / shorted out also!

[scotto]

Thanks guys. Was traveling today. I'll have a look tonight.

[scotto]

172 on pin 1 and 191 on pin 6. Plate resistors measure correct at about 100K. Still looking...

[scotto]

Nothing on 3 or 8.

[scotto]

I get .8 on the 1k5. Would that do it?

[scotto]

.8 K just to be clear

[martin manning]

Lift one end of the 25uF bypass capacitor in parallel with it and measure the resistor again. If it's out of tolerance replace it. If the electrolytic caps have not been replaced they are past due.

[scotto]

Will do. Electrolytics are up to date.
thanks!

[Structo]

Could also be the 1M Volume pot.

I had an amp that should have been crystal clean but was distorted when the volume was turned up.
Preamp Volume pot was defective.

[scotto]

Thanks Tom. this one's dirty at all volumes. I'll try the resistor tonight when I get home. Fingers crossed

[Structo]

Yeah the weird thing was it was a NOS Bradley Allen pot.
It's jumped in value around the 10:00 position.

It was a clean amp so it was weird when it distorted.

[scotto]

Resistor was low with the cap off so I replaced it. Works fine now, nice and clean. Many thanks to all who chimed in and helped me out of the woods!!! I love the way folks help out on this forum. I can't get into the garage thru Google any more but thankfully I was able to get back in thru Yahoo. Would have been lost without you guys!