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Old 11th October 2011, 04:20 AM   #1111
tubekit is offline tubekit  United States
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@ Printer2:
Looks like it's between your second stage and phase inverter.

Do you want to put it somewhere else? If so, why?

Or are you asking for confirmation that this is where it best goes?

Carvin puts their tone stack right after the master volume. Most Fender and Marshall are the other way around. Carvin's design gave me the courage to give that design a try (which is really the only place the tone stack can go in my design without messing up something else).

You've got a choice. But where are you getting your distortion, if any?
You want tone to follow distortion, right?
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Old 11th October 2011, 04:53 AM   #1112
tubekit is offline tubekit  United States
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Default What's your filly tranny? or Dual pots? Cool.

@ The Gimp:

Looks like maybe you've got five gain stages, too, like I do.

But you've also got five filaments. What are you using to heat all those tubes?

Also, I've considered using a dual-pot to tame the volume somewhat when gain is up. Is that what you've got there in pot #3 (left to right)? Or do I see seven pots, not six? And TWO duals (#1 and #4)?

Please enlighten us on this. (Apologies if you already did and I haven't read it.)

If there were more time, I might experiment with taming the dry signal even more and mixing it with the reverb return before going into stage 3, as you evidently are doing, but I'm concerned about fiddling with something that more or less works this late in the game.

I've still got to build up some callouses and practice all the clams out of these pieces I've mentioned before the end of the week if I'm to make an MP3. As it looks, I'll likely have raw, bleeding fingers before I have a clam-free act.

Can I submit just the good sections?

Like from midway in one phrase to midway in the next?

(And just trust everyone's ADHD to smooth out the edits.)
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Old 11th October 2011, 02:59 PM   #1113
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Quote:
Originally Posted by tubekit View Post
@ Printer2:
Looks like it's between your second stage and phase inverter.

Do you want to put it somewhere else? If so, why?

Or are you asking for confirmation that this is where it best goes?

Carvin puts their tone stack right after the master volume. Most Fender and Marshall are the other way around. Carvin's design gave me the courage to give that design a try (which is really the only place the tone stack can go in my design without messing up something else).

You've got a choice. But where are you getting your distortion, if any?
You want tone to follow distortion, right?
You can look at the tone position in two ways. After your distortion stage you can shape the distorted sound for the tone you want or before the distortion you can cut the bass and cut treble so if you really crank it the sound does not turn into mush.

I picked up a small console radio from a thrift shop on the weekend and used it to play around with the 6AU6. I never used pentodes in the preamp yet (real new to this tube thing) and heard they can sound nice but would like some signal hitting them therefor my triode before it. I am finding if I have my Telecaster turned up (not a high output guitar) and want it clean I have to keep the input volume down to 1 or 2 ans still have the gain I want when turned up to 10. Probably should have built it with low and high input jacks, live and learn. Dropping down the cathode resistor to get one volt on the 6AU6 sounds nice but you can forget about any cleans from the amp then.
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Old 11th October 2011, 03:20 PM   #1114
TheGimp is offline TheGimp  United States
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The allied transformer is rated at 2.5A@6.3V.

2X 0.72A for the two 6DX8s = 1.44A
3X 0.45A for three 6GH8A = 1.35A
Total heater current is thus 2.79A out of available 2.5A so I have added an additional transformer to offload one or two tubes.

It was marginal (2.49A) till I added the Reverb, which also busted the budget.

The first dual pot has section 'a' for the gain after the tonestack. The 'b' section is for the gain after the third gain stage going to the PI. This controls how sensitive the amp is to overdrive. Both of these pots have a resistor in series to give me more control over the ratio from each takeoff.

The second dual pot is the PPIMV master volume control. This allows one to control volume independent of overdrive sensitivity.

7 Pots total, plus bright switch. Gain, Treble, Bass, PPIMV, Trem Rate, Trem Depth, Reverb strength.
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Old 11th October 2011, 04:14 PM   #1115
tubekit is offline tubekit  United States
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Quote:
"Both of these pots have a resistor in series to give me more control over the ratio from each takeoff."
Yes, I had exactly the same thought when I considered using a dual pot for the distortion gain with b side wired in reverse to scale master volume ahead of (or across) the master volume pot to counteract the gain setting. I may still implement that in a version of the amp that isn't trying to beat the price target.

That's a lot of heat you're generating there. And I heard that "bust the budget" part of it. That's why I asked.

But then, you do have quite a few more gain stages than I do.
I'm not familiar with your circuit but it is clearly much more sophisticated than mine.

Triode-pentodes do have an appetite for heater current! That was a major design limitation that I was aware of going into this. And the reason I almost went limp at the knees when I saw the specs for the 6KE8: 0.4 A! My 6EB8 is already taking 0.75A, and I wanted to use a 1.6 Amp transformer I have from which I get much of my savings. The 12A6 beam power output is a miser with heater current, using only 0.15 A!!! (Compare that to a 6L6 which uses almost an Ampere!) It's 12 volts, so that equates to 0.3 A at 6.3, but that's still pretty frugal. But there just wasn't room in there for two 6EB8s AND the 12A6. and then I saw the 6KE8 in an assortment of tubes I bought at eBay and looked up it's specs. O Happy Day!

I've got another tube that uses 0.15 at 6.3 volts that will just fit into this fillament tranny, too, and it produces a real nice distortion rich in second harmonics, but it will have to wait for later. It also could make a great vari-mu compressor stage. I overreached and tried to get it to do both. Not enough time to get that design right for this amp challenge. I spent weeks on it before abandoning it for the simpler design due to weird oscillations.
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Old 11th October 2011, 09:02 PM   #1116
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I can't imagine shaving off $25 in order to have reverb, well not unless I did all my part sourcing here and there. When I started I decided to stick with two venders in order to keep the shipping costs down. (Allied Electronics, Antique Electronic Supply). Oh I would love to have some reverb happening. Next amp. Unless something obvious comes up this is what I will wire up.

Click the image to open in full size.
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Old 11th October 2011, 10:09 PM   #1117
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Quote:
Carvin puts their tone stack right after the master volume. Most Fender and Marshall are the other way around. Carvin's design gave me the courage to give that design a try
In my 5 tube (8 tube sections) design I started out with the tone stack after the gain pot which is between the first and second triode gain stages. I played with the order of things several times before settling on the tone stack after the master gain which is between the 4th gain stage and the PI. This seems to allow the best compromise between clean and cranked to meltdown tones.

Another "ingredient in the secret sauce" is an "L pad" between the OPT and the speaker. This allows the amp to run wide open at 15 watts but the power applied to the speaker can be dialed back to 1 or 2 watts to avoid the noise police!

Quote:
But you've also got five filaments. What are you using to heat all those tubes?
Secret ingredient #2, I wired them all in series and hung the string across the B+ supply. No heater winding....no heater transformer.

Secret ingredient #3, I stuck a tone control in the feedback path. Not as useful as I expected, but good for some rather unusual tones.

I was still experimenting with that one when I had to leave town. I might have a little time when I get back if work doesn't expect me to sleep under my desk at night after being gone for nearly 3 weeks!
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Old 12th October 2011, 03:44 AM   #1118
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So there goes my credibility. You know when I say, 'This is the circuit I will be making'? Just believe it once you hear a clip of the amp.

I pretty much did what I wanted with my test amp and decided to dismantle it, wires and test clips all over the place. Well I noticed that I was playing with it missing the bypass cap on the 6AU6. Might as well see what it sounds like with it. Hook it up and grab the guitar... ...oh my, it has much more effect on gain than on a triode. Back to square one.

Cathode and screen values needed to be much different, decided to put a switch in to change the plate resistor between 100k and 220k just for kicks. Much more chimey. I have a problem with the low E string though. And I probably have to dump some gain somewhere. Talk about cranked to meltdown. Maybe the tone stack before so I can dial out the bass and cut some of the signal before it hits the pentode. The ears got tired so I am giving it a break for a while. And I thought I almost had this wrapped up.
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Old 12th October 2011, 04:24 AM   #1119
TheGimp is offline TheGimp  United States
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Triad Utrad F-13X

6.3V @ 0.6A

I should be able to parallel the windings. Otherwise I'll have to power one tube separate from the rest.
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Old 12th October 2011, 04:35 AM   #1120
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In my 4 tube design (4 stages total) I wound up with the pentode first (similar to a 6AU6) followed by the tone and volume controls then the triode stage (1/2 of a 12AX7).
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