Realistic Carnival 6V6GT Tube Amp Help

[DRH1958]

Agree with the speaker change. There's little chance you'll get much good reproduction from that 8". There's a good chance that could be part of the problem as far as breakup of the output. One strategy for getting better sound is getting a larger speaker that is also more efficient. If you get a speaker that has an efficiency rating that is 3dB higher than the previous one, it effectively doubles the power delivered to it. The 56k for the grid stopper is fine. Does it sound better than before even though it's distorting?

I find it a bit strange your bias voltage on the second stage dropped by a third of a volt with no changes to it. Pin 3 used to be 1 volt and now it's .66v but the plate voltage didn't effectively change. That could lead to more distortion since it throws off the bias. Any clue as to what might have happened? Is everything still the same as before? Is the 10uF (C2) bypass cap and R9 still solidly connected to ground?

Try adjusting the phono-tuner volume control to see if there is much change in sound. Play a chord and adjust it while playing. Changing the setting might change the sound of the amp some or it might not. Make sure the third(bottom) lug still connects to ground.

One last thing and I think I mentioned it before, this amp is probably only putting out about 3-4 watts with those low voltages on the 6V6, so no matter what, you will not get much clean power under any conditions. 4 watts just won't get it done.

[misterc57]

.... Does it sound better than before even though it's distorting?

I can only comment on the tuner-phono path. Much less distortion, but also seems like less volume now on this path. I am able to turn up the iPod to higher levels (I did not measure the level) and there is no distortion like there used to be.

I find it a bit strange your bias voltage on the second stage dropped by a third of a volt with no changes to it. Pin 3 used to be 1 volt and now it's .66v but the plate voltage didn't effectively change. That could lead to more distortion since it throws off the bias. Any clue as to what might have happened? Is everything still the same as before? Is the 10uF (C2) bypass cap and R9 still solidly connected to ground?

My bad here... the reading difference could be related to where I am reading from. Having a hard time clipping pin 3 for readings so I have been clipping either the leg of the R9 or the C2 (Will check the ground again) thinking they would represent VDC at pin 3. I should take readings again directly on the pin.

Try adjusting the phono-tuner volume control to see if there is much change in sound. Play a chord and adjust it while playing. Changing the setting might change the sound of the amp some or it might not. Make sure the third(bottom) lug still connects to ground.

I did adjust the p-t volume while playing guitar and heard no changes. Will check that pots ground again.

One last thing and I think I mentioned it before, this amp is probably only putting out about 3-4 watts with those low voltages on the 6V6, so no matter what, you will not get much clean power under any conditions. 4 watts just won't get it done.

Interesting! I notice that the 5F1 has much higher voltages.

Well, I have a lot more testing and readings to take. May be a couple of days before I get a chance.

Thank you all, especially DRH1958, for all the help. This has been a great learning experience.

MC

[misterc57]

Pin 3 is at .989 volts (now that I am reading directly on the pin).

I hooked the amp up to an enclosed 12" Peavey cab... I have to say this amp sounds amazing, breaking up where you would expect (volumes above 7) and really sensitive to the guitar volume knob. I am surprised at how good it sounds and how loud it can get as well. The tone pot does a really good job as well.

So what do I do now? Here are my thoughts and questions.

Should I keep the second RCA input? I doubt I would ever use it that way, do I convert that to a second guitar input like the 5F1, what would I gain from doing this? Do I remove this input all together and place a panel mounted fuse in its place?

Do I modify the second stage of the 12ax7 to be identical to the 5F1 (replacing C2 and R9 with a 1.5k resistor)? Amp sounds good now, what would I gain from doing this?

Thank you! MC

[Jazz P Bass]

So what do I do now?

Sell it!

To me.

[DRH1958]

Glad to hear that pin 3 is at a volt, where it should be. If you like the amp's performance, I wouldn't make any changes, including not changing the second stage. Don't fix it if it ain't broke as they say. You sound like you have good range in your volume control. I would be tempted to use that second RCA input as a fuse holder as this will give you good access to it. Disconnect R6 from Pin 2 or where it connects to R7, however they did it as you won't need that circuitry any more and you could now change R7 to 1.5k. It now becomes a grid stopper. Or you could eliminate it altogether and see what it sounds like first before changing it.

If you change the input network to the Champ style, one jack will provide a hotter signal than the other. Jack #1 will be a higher signal and jack #2 will be the input you have right now. If you look at the schematic, plugging into #1 will effectively put both grid stoppers in parallel, reducing the resistance giving a hotter signal. #2 sends the signal through your 56k and will be the lower input. Here's a good explanation if you want more. In the article, they call the 1 meg R3, the a "grid load" resistor. Don't let that confuse you, I've always heard it called the grid leak resistor. Scroll down to hi-lo jacks: Classic Tube Amps - The Preamp

[misterc57]

Some pictures

Thought I would post some pictures of the amp.

I have since removed the back speaker terminal and used that space to install a fuse and 1/4" phone plug for speaker out. I also drilled a hole in the back to install a 4 to 8 ohm toggle switch. The amp has a cage cover that is not in the pictures. I need to do something with the bottom of the chassis as it is completely open.

[misterc57]

With guitar plugged into the MIC input, I have noticed that there is a slight tone change when adjusting the tuner-phono volume pot. I cannot explain the difference in sound but I prefer the sound with this volume pot maxed at 10. What I am curious about is why this effects the tone.

[DRH1958]

With this vol maxed, you are changing the grid leak resistance value of the second stage by adding the 500k value of this vol in series with R6. These two series resistances are in parallel with the series connected R7 and the R1 volume control because both are connected to ground. You are changing the overall grid leak resistance so the signal being input to the second stage is a little stronger because of the higher grid leak resistance. It also changes the frequency response a little by this changing resistance acting with C5 coupling cap. These two values(grid leak and C5) determine the frequency response of this stage along with the output impedance of the first stage. Remember in an earlier post I asked you if changing this pot's value made a difference? This is what I was getting at back then. I thought you could get different sounds by adjusting the phono-tuner vol. I suppose re-working the input stage changes things enough to now make a difference.