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This is my work room, it's in the storage room but beats in the garage. Small parts bin in the room: Tube parts and excess capacitors etc. in the garage: Don't have a lot of equipment and don't have room for more equipment. Have to cycle test equipment depending on the work I do. I...

The PP is only 30W max and no lower primary resistance option. It's not useful for me.

Old pot does not cause hum, period. There must be something else going on. Wires got moved, loose ground wires, too many possibilities. Have to follow the logic. I think the best is to have the assembly drawing, check all the wires to make sure they are in position as drawn. [Mod Edit] Look at...

Yes, it's the CTS pot I refer to. Actually it's my friend D. Allen of D Allen pickup that told me. CTS 250K pot is actually more like 220K to 230K. That shaves off a little sting from the Strat pickup to make is a little fatter. Like capacitor, you really need to measure the value and test...

Now, I did not expect that. A tone pot causing hum. You sure you have the wire exactly the same. But anyway, if it is gone, it's gone.

Something unrelated to your amp. If you are old enough and use effect pedals back in the older days, you would notice if you string a few pedals, you guitar sounded very muddy even you switch out all the effect. I used to think it's the connection and connector or switch. Actually what happened...

As I said, go to Music Electronic forum and ask on the caps and resistors and modification. Even though I designed guitar amps, I have limited experience as I did not spend my life on it. I am more into theory, different type of electronics. Guitar amp does not need theory, it's a lot of trial...

Sound like whoever worked on the amp, it modified back to 5A3. I would change the 300ohm back to 250ohm. Don't worry about the power dissipation, it works. People have been pushing the tubes pass the spec and they live a good long live. 250ohm gives you a bigger class A region. As I said, I...

Basically the same circuit with slight change in values, my comment still applies. You can see the Bass tone cap is 0.01uF rather than 0.005uF in 5A3. Also, the input resistor is 50K vs 75K in 5A3. 5B3 you have is a little more bassy in both ways. The higher the value the resistor at the...

I meant don't have to change the capacitor, it's designed for that. It is really high pass filter. eg. if the grid resistor is 250K and cap is 0.05uF. The high pass is 12.7Hz. This is good for even bass guitar. If you low the value, you might cut the bass. As I said before, the two cap at the...

Guys, I am happy to be wrong. I assume all ceramics drift!!! So the next question is why are we still using film caps for low values values like below 0.0022uF?

Here is the schematic for your amp, it's 5A3 that's for your year. I save the un-marked up schematic for your reference so you can download it. You see the two caps I marked TONE? You change those two, you can change the sound to your taste. You amp is cathode biased, it will bias to the...

Ha!!! Tell me more, I love to be wrong on this.

One more thing, if you really want to get into this, go to this forum:http://music-electronics-forum.com/activity.php? This is a forum for serious guitar amp people. There are knowledgeable people there that can give you insight what to do. I used to be on that forum until I lost interest in...

I am going to say something OP must not like to hear. I had been a guitarist for over 10 years, performing in concerts, gigging, on TV and radio when I was young. I successfully designed quite a few guitar amplifiers with power scaling, channel switching high gain amplifier. I know how a good...

No, I was responding to your post on your experience of ceramic cap as output coupling cap. Nothing to do with the feedback cap. I know using COG/NPO cap for feedback WORKS. I use them in my SS amp and I am getting 0.0035% THD at 60W 20KHz. Way better than any tube amp can do. That's not my...

You use it for output? What value you use? Are you using COG/NPO? Output coupling cap usually needs higher value above 1uF. I can't find any COG/NPO this value.

Anyone mention about matching the two output tube? If the tube is not matched, it will hum. I don't know this old amp, Fender had balance adjustment in their Black Face and Silver Face amps. You adjust the pot after you change the tube......by adjusting the hum out. So before doing anything...

Very interesting result. This is particularly good as Bateman actually design capacitors. I used to think about voltage coef. only, but he added the loss tangent. Looks like the COG/NPO are almost as good as the best of film caps. ( about 3db different when measuring at -126dB!!!) That's more...

This is actually my question: Is NPO/COG ceramic caps have as low distortion as the film caps? I want to put a low pass filter to roll off some highs. I don't mind the value drift off......so if the poll frequency is 900Hz instead of 1KHz, it does not matter to me. But distortion matters.

Ha ha, he should be thankful he got one that is definitely an improvement. Changing a few things is expected. A lot more meaningful than roll the 12AT7 in. Hey, it's a lot better than drilling the chassis to fit a 6SN7!!!

Yes, from looking at the plate curve, if you lower the plate voltage to about 130V, use lower plate resistor, the curves should be more even. But the output swing is very limited. So that's another draw back. Thanks, I'll look into 6CG7/6FQ7, :thumbsup::thumbsup::thumbsup:I don't like the big...

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What do you mean by working on it? I hope just changing the filter caps. You don't and should not change the coupling cap, this is part of the original circuit that make the value of this antique amp!!! I would just change the big filter caps and NOT touching anything else. You should not change...