'68 Bassman amp volume

[Doc Stitches]

here are the pot photos :

[Doc Stitches]

Normal channel is around 2/3 volume and great tones.

Bass channel is still distorted a little and very low volume, ( like #1 or less ). No volume until #5

[Chuck H]

First:

Playing amp on both channels now, Bass channel is louder and very clean.

Normal channel is like volume #1 when set on #10 as well as a little distortion.

Then:

Normal channel is around 2/3 volume and great tones.

Bass channel is still distorted a little and very low volume, ( like #1 or less ). No volume until #5

I think we need clarification so we know where to look.

[Doc Stitches]

Clarification ? ... What would you like to know ?

Also I have a 10K resistor on bass pot of bass channel.

Is this acceptable ?

I am ordering some 8.2Ks

[eschertron]

Clarification ? ... What would you like to know ?

Also I have a 10K resistor on bass pot of bass channel.

Is this acceptable ?

I am ordering some 8.2Ks

I think Chuck's asking about where the first post says bass channel loud and clean, then second post says still distorted. The posters who are 'playing from home' rely on specific and accurate details to suss out where to look (not being able to twiddle and listen themselves). That's all.

[Chuck H]

First you said it was the normal channel that was low volume and distorted and then later you said it was the bass channel that was low volume and distorted. Did this change between the two posts I quoted from or is one of the quotes inaccurate. Are we dealing with only one channel that is exhibiting grossly low volume and if so which one? Or has either channel been more problematic than the other at different times?

[Doc Stitches]

sorry for the confusion

As of now, both channels have low volume on #10 ( about 30% ) with tone controls on 6.

Both channels : volume begins at #5

Amp is very quiet

All tone controls are quiet and functioning normally.

I am using an original, 1964 deluxe reverb 8 ohm speaker, plugged into the speaker jack.

[The Dude]

Have you verified the speaker is good? Maybe try it with another amp or try this amp with another know good speaker.

[Chuck H]

So... The tone controls on both channels are working. First both channels were very low in volume. Then the normal channel was almost working but the bass channel was much lower in volume. Then the bass channel was almost working but the normal channel was much lower in volume. Now both channels are, again, very low in volume. Now, we don't know all of the efforts that have happened in between these different incarnations of relative broken-ness, but...

Ok... Here's where "my" logic is taking me. Since the tone and volume controls work (relatively) the problem is ahead of the preamps. Since there have been two occasions when one of the two channels was almost loud enough let's not worry about the PI for now. That only leaves the mix circuit where both channels meet the PI input. And those traces are under the board. Did you ever check for continuity of those connections and did you ever touch up the ugly solder joints?

Here is the layout. I've circled the connections I would suspect first in red. Remember that some of what is supposed to be connected to these will be under the board. Hopefully you can see the lead ends poking UP into the eyelets. At the very least a meter should be used to confirm continuity.

[Doc Stitches]

Deluxe Reverb speaker works great with the 64 Deluxe Reverb amp combo.

[Doc Stitches]

Thanks for layout details Chuck

I did touch up the worst solder joints. When I started this project none of those 3 eyelets had ends poking up.

Remember, whoever had this amp before me partially gutted it and attempted modifications.

I wonder what the bottom of the board looks like ?

I failed to see that middle eyelet of those 3 ( highlighted eyelets had to be connected )

I'll try to get to it tonight and get back to post results.

[Doc Stitches]

Ok, amp is sounding like a Bassman should.

But ..... both channels have a very loud hum. I'll get the drum stick out tomorrow and recheck tubes.

Had to turn the variac way down to stop the hum.

[Chuck H]

Be sure to check the bias balance circuit to be sure it's still providing appropriate voltages and has been twiddled for lowest hum. After that I might suspect an iffy power tube. After that I might suspect an iffy preamp tube. After that I would suspect a loose or missing ground. BE SURE TO CHECK THE BIAS CURRENT NOW!!!

[Doc Stitches]

I was wondering about the bias recheck. Will check all tomorrow.

[Doc Stitches]

-47v on both tubes ( pins 1 & 5 )
475v on both tubes ( pins 3, 4 & 6 ) ... balance control doesn't change hum
changed power tubes ... still hums. ... Tried different preamp tubes ... still hums
all tubes in but no v1 ... hums
all tubes in but no v2 ... no hum
all tubes in but no v3 ... hums
all tubes in but no v4 ... no hum
When I turn off the amp there is a quiet motorboat putting sound
Still have to recheck for loose/missing ground

Does this photo help ? when the previous owner added the grounded cord this in how he wired the ground switch
Is it OK ?