Dual Single Ended Output

[hesamadman]

Im going to use one of these extra Hammond 290ax PT that I have lying around. The 290ax is a replacement for the Princeton, Princeton Reverb, and Tweed Deluxe. Im thinking I would like to do a dual-single ended 6v6 output. This is mainly for breadboard use and tinkering. I was wondering if anyone knew of an amp with one of these types of power amps that I could study. I know Dave Hunter included one in his book "The Guitar Amp Handbook" but no schematic was given. Only the layout.

[DummyLoad]

solid state or tube recto?

[hesamadman]

I have a 5v tap on the transformer. Ill probably do both just for fun. Its just going on the bread board. 

[shooter]

I did a SE dual el-84 a couple years back, that started as a 6v6 dual.  bought all the parts thinking 6v6 but needed the 6v's for a repair so I just sub'd the el's.  used a wse-15 OT a 5u4 tube rec. B+ about 295.

Was liked quite well by a handful of players and finally bought by one of them, anyway, fwiw

[hesamadman]

I did a SE dual el-84 a couple years back, that started as a 6v6 dual.  bought all the parts thinking 6v6 but needed the 6v's for a repair so I just sub'd the el's.  used a wse-15 OT a 5u4 tube rec. B+ about 295.

Was liked quite well by a handful of players and finally bought by one of them, anyway, fwiw

That's awesome. I would very much like a se dual el84. Got a schematic for the power amp?

[sluckey]

That's awesome. I would very much like a se dual el84. Got a schematic for the power amp?

The schematic is attached to his reply.

[hesamadman]

Thanks guys. I don't know how I miss stuff like that all the time.

[hesamadman]

Thanks for the Schematic shooter. Im looking at the transformer you suggested. Im also considering a Hammond 1750B. Which is a 10 watt SE transformer fender replacement. Im considering the hammond because a: i like to stick with hammond and b: I like to cut down on ordering from as many places as possible. In the end If im ordering parts for the amp from hoffman and my transformer supplier, I can have about $35-$40 in shipping so adding to another supplier, thats another $15.


So I guess im wondering what the trade off would be going from the weber 15 to the hammond 10?

[kagliostro]

I don't know if this can be of your interest (it is a very clean amp)




1 ecc83 tube + 2 x 6V6 tubes

Here full documentation about construction (layout and other)

http://www.ampmaker.com/infocentre/forum-29-page-1.html

Here a British overdrive amp



1 ecc83 tube + 1 x EL84 or 1 x 6V6 tube (swapable)

Here full documentation about construction (layout and other)

http://www.ampmaker.com/infocentre/forum-31.html

if you use adequate PT and OT you can use paralleled final tubes

K

[shooter]

kinda funny cuz till that build I had used all hammonds or edocrs, but like you, I think weber had 90% of my missing parts so......
If you wanna go crazy I also built a quad SE el-84 amp with a 6sn7 driver, no pre but it wasn't much louder and was way more problematic getting all 4 tubes to cooperate.

[hesamadman]

I don't know if this can be of your interest (it is a very clean amp)

Thanks Kagliostro. I may consider these builds at some point. Right now I am very interested in a dual single end el84. Im kind of playing around with different output tubes and such right now.

[hesamadman]

kinda funny cuz till that build I had used all hammonds or edocrs, but like you, I think weber had 90% of my missing parts so......
If you wanna go crazy I also built a quad SE el-84 amp with a 6sn7 driver, no pre but it wasn't much louder and was way more problematic getting all 4 tubes to cooperate.

Im actually kind of working my way up a ladder of builds. Im a big fan of el84's. I love the Blues Jr. and I love the AC15 and 30. I know this SE El84 will have a whole different feel but im kind of going that rout as of now because I dont think the transformers I have can handle dual el84 and a phase inverter. Im not sure. I need to learn a bit more about sizing my circuits and getting the appropriate transformers for the job. I have two of the Hammond 290ax ( http://www.hammondmfg.com/pdf/EDB290AX.pdf )


REALISTICALLY.... I would like to see dual 12ax7 and dual EL84 in this build. My goal would be to throw a pre amp volume in the middle of the first triode and a treble and bass in between the two halves of the second triode and a master volume at the end of the preamp right before the power amp.


Do you think this transformer is capable of holding up to this setup? If not, I will do a tone control only and a volume somewhere else. Maybe at the end. Maybe in between the two halves of the one 12ax7. I know this transformer is a replacement for a deluxe, which (correct me if im wrong) consists of a 12ay7 in the preamp. 12ax7 phase inverter. Not sure of the type. Just know its not long tail. and two 6V6GT in parallel.

[kagliostro]

May be this (adding a power tube in parallel) ? You can use a pair of el84 instead of 6v6 if you prefer








Or this P1 / High Octane switchable (it already uses el84)



or, if you want to experiment with pentodes



same with more gain



K

[PRR]

> Hammond 290ax

That's 325V per side. With SS rectifier you will be above 400 Volts of DC.

The EL84 is rated closer to 300V. Yes, we all use them at 350V, and new-production *may* hew to the 7189's 400V spec.

But in an SE amp, more voltage is NOT more Power. You are limited by Plate Dissipation.

Assuming a hollow-state rectifier or a hefty dropping resistor to get down near 350V DC, the PT has 350V*0.081A or 28 Watts of DC available. The EL84 is rated 12 Watts. You probably have a Watt in the screen and a Watt in the cathode resistor, another Watt in the preamp. Not a bad fit.

At an assumed 335V plate-cathode, and 0.078A total plate current (two tubes), 335V/0.078A suggests a 4,295 Ohm load (4K for all practical purpose; 5.4K is not wrong).

290AX has 2A of 6V power. EL84 is 0.76A, 12AX7 is 0.3A. Two and two adds up to 2.12A. If _not_ using the 5V winding (no vacuum rectifier), I would overlook the small excess.

But two 12AX7 can be a killer preamp and push-pull driver. Push-pull EL84 is good for 18 Watts output. And your OT will be cheaper and lighter. I'd just do an "18 Watt" on that PT. Tonestack, NFB to taste.... it does not have to wind up a mini-Marshall.

[hesamadman]

290AX has 2A of 6V power. EL84 is 0.76A, 12AX7 is 0.3A. Two and two adds up to 2.12A. If _not_ using the 5V winding (no vacuum rectifier), I would overlook the small excess.

If I read the data sheet correct, a 6v6 is .45A. So I could get by with two of those and two 12ax7 if I use a solid state rectifier. Is that correct? At this point I am really trying to utilize the 290ax since I have two of them.


Im not dead set on the el84's now that Im thinking about it. I can do an el84 amp after I utilize these 290ax PT. Once I decide on a design, im going to build two side by side with some minor differences. So since im at the drawing board again I need to determine what power amp design to use, using the dual single ended 6v6 (if you think thats a better option for my PT). And I will have to find an OT to accommodate also.


Each build I focus on a certain aspect of the amp that I want to learn more about. This one I will focus on sizing and matching transformers to my design ideas that I come up with.


Im to the point to where im trying to learn to size transformers accordingly. I should probably find and print out some tube data sheets to help out.


Also, I only suggested this ( http://www.hammondmfg.com/pdf/EDB1750B.pdf ) because its the largest SE OT I can find from hammond.

[hesamadman]

I don't know if this can be of your interest (it is a very clean amp)

Im considering the dual SE 6v6 design (power amp at least) you suggested since my PT may not be suitable for the EL84's I originally wanted.

[kagliostro]

As PRR say, if you don't use the 5v winding the transformer can afford the 120mA of consumption in excess

ad if you swap to 6V6 the consumption will be within PT specs

but you have one other way to use el84 tubes with a bit of complication on construction but possible

Assuming you use SS rectify you can use the VVR circuit shown in one of the schematic I posted, so you can split a part

of B+ drop to a resistor and a part to the VVR (using a resistor in series with the pot as to avoid the B+ reaches his maximum level)

(or use 6P14P tubes instead of the el84, they are the same tube with a bit more plate dissipation and higher B+ bear)

then, as to avoid an excess of consumption on the 6.3v winding, you can supply the power tubes from the 6.3v winding

and the preamp tubes using a doubler on the 5v winding, you can tame the excess on voltage (5v x 1,4 x 2 = 14v) connecting the

preamp tube heaters for 12.6v and using series resistor to drop the excess of voltage,

doubling the 5v you lost 50% of disposable current, but you have still 1A disposable,

the preamp tube consumption at 12.6v is 150mA so you can use also 4 preamp tubes without problems

Told that, the voltage of your PT is more suitable for 6V6 tubes

K

[hesamadman]

I don't think I'm quite experienced enough to make this PT be more suitable for the el84. I think I'll use the 6v6 but I'm just hoping to get a second opinion on my OT choice or even a recommendation.

[kagliostro]

A doubt appears on my mind


you are looking for a Dual Single Ended Output schematic


isn't that you are referring to an amp that has two SE OT each with his tube ??


I tried to find info about the layout you indicated is present on Dave Hunter book


but I wasn't able to find


K

[hesamadman]

I believe the top schematic you posted is a dual SE 6v6.

My understanding is that it's two tubes in parallel with no PI rather than push pull. And is driven by only one OT.

[kagliostro]

OK, that architecture is a PSE (Paralleled Single Ended) that uses only one OT


I was thinking you refers to a double SE that uses 2 OT, one for each tube


K

[hesamadman]

Sorry. I learned it as the term "Dual Single Ended" from Dave Hunters book but Parallel Single Ended makes a little more sense to me. So I found out the Hammond 1750B is a reverb driver for vibro king.

[hesamadman]

Ok Guys,
So Im changing things up a bit than when I started this thread. To accommodate my PT, I will be using a PSE 6v6 power amp. Two things, I need suggestions on the power amp and OT. Ill give a brief description of my goal on this amp and hopefully you guys can give me a direction on the power amp and OT.


I will be using dual 12ax7's. I plan on using at least a bass and treble tone stack (if not a full bass, mid, treble tone stack). I like a good rockin lead tone so I will be concerned with getting a nice gain out of the amp. Im going to throw this on the bread board and put my pre amp together and tinker with it all before I put it in a chassis, but I am very limited on knowledge in the power amp department.


I really like Hammond transformers. So far they seam to be the most affordable. I can not find anything though. I guess I will take whatever other manufacturers you suggest for the OT.


What are some things I need to look at when matching an OT to a design. For instance, Kagliostro posted a schematic at the top with a PSE power amp. How would I go about matching an OT if I were to use that design?

[PRR]

> 1750B.... its the largest SE OT I can find from hammond.

125ESE is 15 Watts, and a big hunk of iron. 125GSE is 25 Watts.

1642SE is 75 Watts and 28 pounds.

Ah, I see.... you are just looking at their "Tube Guitar Amp" line. No, that won't go over 10 Watts because why would you build and sell a single-ended guitar amp that big? As soon as you need two power tubes, going push-pull allows an OT which is VERY much smaller (and cheaper) than a big SE OT, even counting the cost of a phase splitter.

So no mass-market money-making g-amp has ever featured much more than 10W in SE.

(Gibson did have a two-6V6 in SE, but not worked hard, so still probably only 10W; and i suspect they were using-up surplus chassis or discount OT from a collapsed radio product.)

The 125*SE series "is" guitar-amp quality. Not too bad, and not too good.

The '"Classic" - Single Ended' series is "too good" for guitar. The 125*SE series will go to about 75Hz at full power, the Classics are rated for 20Hz. Guitar only goes to 82Hz (or a few semitones lower), you don't need 20Hz (and do not want to pay for it or carry it). Guitar speakers aren't that good at 82Hz, you usually want some bass distortion to put bass overtones higher in the spectrum where the speaker will throw them.

If you want "the most" in a two-tube SE with 125GSE you need about 60 Watts worth of tubes. Five 6V6, two hot 6L6/EL34, or two 6550/KT88. And a huge PT.

One 6L6 or two 6V6 with a 10W OT is a more practical project.

If you just like HEAVY METAL, you can use the 1642SE ($321!!) at upwards of 150 Watts to get more guitar-type bass performance. You need 400 Watts worth of bottles suitable for 1400 Volts 0.28A.

Type 5-500A may be suitable.

Used 5-500As are available for $400.

[hesamadman]

I'm not looking for a ton of power. 10 is absolutely fine. I didn't mean to come across as needing a ton of power. As a matter of fact, now that I'm thinking about it, I wouldn't even need two 6v6 to get 10 watts right? A single could do that I assume?

I mean all I'm trying to do is get the most out of my PT that I have. So I should have probably thought a little more before posting. I just thought the pse 6v6 sounded interesting but I didn't know the cost was so high in transformers to suit.

So I guess I'm at the beginning again. I just know I want more than 5 watts. Is this going to be possible to do in a SE build and not involve a huge OT and cost an arm and a leg?

If not, I'll do push pull 6v6 and a PI in place of my second 12ax7

[DummyLoad]

single 6V6 nets close to 5W, downhill with a tailwind 5.5-6W if you beat on it hard...


a single 6L6GC or 6550 is the ticket for 10W. hammond 272BX PT and 125GSE @ 5K - optimum load is closer to 4K - the heyboer TO11S  is a good fit 4K load into 4/8 and designed for 6L6. the hammond 272BX should make about 375V @ 90mA if you tap the B+ at a second filter - it's single tube class A so you'll want clean power. to do that you filter as much as you can stand, unless you like buzz and in a high gain amp, you don't want buzz...


--pete

[DummyLoad]

> 1750B.... its the largest SE OT I can find from hammond.

125ESE is 15 Watts, and a big hunk of iron. 125GSE is 25 Watts.

1642SE is 75 Watts and 28 pounds.

Ah, I see.... you are just looking at their "Tube Guitar Amp" line. No, that won't go over 10 Watts because why would you build and sell a single-ended guitar amp that big? As soon as you need two power tubes, going push-pull allows an OT which is VERY much smaller (and cheaper) than a big SE OT, even counting the cost of a phase splitter.

So no mass-market money-making g-amp has ever featured much more than 10W in SE.

(Gibson did have a two-6V6 in SE, but not worked hard, so still probably only 10W; and i suspect they were using-up surplus chassis or discount OT from a collapsed radio product.)

The 125*SE series "is" guitar-amp quality. Not too bad, and not too good.

The '"Classic" - Single Ended' series is "too good" for guitar. The 125*SE series will go to about 75Hz at full power, the Classics are rated for 20Hz. Guitar only goes to 82Hz (or a few semitones lower), you don't need 20Hz (and do not want to pay for it or carry it). Guitar speakers aren't that good at 82Hz, you usually want some bass distortion to put bass overtones higher in the spectrum where the speaker will throw them.

If you want "the most" in a two-tube SE with 125GSE you need about 60 Watts worth of tubes. Five 6V6, two hot 6L6/EL34, or two 6550/KT88. And a huge PT.

One 6L6 or two 6V6 with a 10W OT is a more practical project.

If you just like HEAVY METAL, you can use the 1642SE ($321!!) at upwards of 150 Watts to get more guitar-type bass performance. You need 400 Watts worth of bottles suitable for 1400 Volts 0.28A.

Type 5-500A may be suitable.

Used 5-500As are available for $400.

https://www.youtube.com/watch?v=fxoxw9Dq6kw

[HotBluePlates]

... I mean all I'm trying to do is get the most out of my PT that I have. ...

Im going to use one of these extra Hammond 290ax PT that I have lying around. The 290ax is a replacement for the Princeton, Princeton Reverb, and Tweed Deluxe. ...

It would seem that "getting the most out of" them would be to use them in the circuit for which they were intended. So a 2x 6V6 push-pull amp.

... So I should have probably thought a little more before posting. ...

No, you did the right thing. It's how this works.

"Peer Review" exists in a lot of fields. It's easier to find the holes in the master plan when it's not your baby.

I should also say I'm lousy at re-purposing tube amp parts. My experience has been that components generally carry specs suited to a particular circuit (or family of circuits); so when I've tried a random power transformer and build an amplifier that didn't closely match the amp it came from, the results have always disappointed me. Usually because there were a series of problems I unknowingly created for myself by using the part in a way it was not intended.

[PRR]

>> extra Hammond 290ax PT that I have
> It would seem that "getting the most out of" them would be to use them in the circuit for which they were intended. So a 2x 6V6 push-pull amp.

Well, a 2x 6V6. The PT doesn't have a strong preference if the amp is SE or P-P. (Until you get into the extreme deep-AB cases.)

> A single could do that I assume?

You can put 12 Watts IN to a 6V6. It has losses, also we measure on a Sine which mostly well short of the peak.

Ideally you could get 50%, or 6 Watts output.

In practice (with real parts) you are doing good to get 40%, or 4.8 Watts.

Yes, there is a datasheet condition for late 6V6 showing 5.7 Watts, but at very high distortion.

If you want more than 5 Watts, one 6V6 isn't up to the job.

Two 6V6 in SE at 9 or 10 Watts is somewhat "more than 5 Watts".

One 6L6 can do the same.

Two 6V6 in push-pull is 14 Watts conservative. Fix-bias can get 20 Watts output.

The nothing-new approach is to steal the whole plan from Fender DeLuxe, Marshall 18 Watt, and other known-good 10W-20W amps. Most will be in-sight of those PTs you have. Most already have known-good OTs at the usual g-amp part suppliers (like our host).

If you really must do something that has never been done before, you can do it. You might find out why it hasn't been done before. (You notice Marty didn't try to *move* Doc's mega-amplifier.)

[DummyLoad]

doug can order the part below for you. i think it takes a couple of extra days, maybe more, but he states you pay the 100 piece price. for 15W SE it's a very flexible piece. he ordered the heyboer trainwreck TW35 OT for me. worth the wait. run your power tube of choice up to 30 watts give or take.   

http://www.mojotone.com/amp-parts/transformers-mojotone-project-output/15W-SE-Output-Transformer-3-5K-4K-5K-primary#.VE3T5iLF98E


whatever you decide, happy hackin'. 


--pete

[hesamadman]

It would seem that "getting the most out of" them would be to use them in the circuit for which they were intended. So a 2x 6V6 push-pull amp.

This is probably the best idea. Ok so it has evolved a good way but I do believe that this is where its going to land. So now I need to find a schematic that uses dual 6V6 in push pull. And I would really like to use one with a long tailed PI rather than a lot of old Fender cathodyne PI. Simply because all my studies have been around the long tailed PI so far.


I did consider this ( http://www.turretboards.com/layouts_schematics/fender/schematics/fender_deluxe_6g3.gif )


I dont know if this new setup will leave me with the capabilities I had hoped, but I would like to have a Bass and Treble control rather than just a tone knob. With only one preamp tube im a little concerned, however this does include a PI which in itself would help my signal loss from such, correct?

[hesamadman]

If you really must do something that has never been done before, you can do it. You might find out why it hasn't been done before. (You notice Marty didn't try to *move* Doc's mega-amplifier.)

Im just trying to do something I myself haven't done before.    Being so new to amp building it may seem like im trying to re-create the wheel, but I just don't have much knowledge of many other amp models and their makeup. I've been playing guitar for 19 years but didnt own my first tube amp until 4 years ago. ha ha And since then, I've built more tube amps than I have ever actually owned before. It's turned into an addiction though. Wish I would have done it sooner but I was a dumb young fella.


Thanks for all the help everyone. I know a GREAT deal more now than I did when I started.

[hesamadman]

doug can order the part below for you. i think it takes a couple of extra days, maybe more, but he states you pay the 100 piece price. for 15W SE it's a very flexible piece. he ordered the heyboer trainwreck TW35 OT for me. worth the wait. run your power tube of choice up to 30 watts give or take.   

Thanks Pete. That OT would have been something to consider. From all the info everyone has sent to me I have learned that a dual 6v6 in push pull will be much more efficient. Sounds like thats the rout to take. 

[shooter]

One of the things I learned here and from musicians about SE vs PP is the tonality of the amp which is as subjective as politics and religion! but even being sonically challenged, i can hear the difference.  So besides cost, efficiency, practicality, there's another parameter for you.

[hesamadman]

So I drew up a schematic. Its included as attachment here.


I used the power and output from a Fender Deluxe Model 6G3 ( http://www.thevintagesound.com/ffg/schem/deluxe_6g3_schem.gif )


I added a post phase inverter master volume using a dual 500k pot. Hoping someone could check my work there on that addition.


I also put together a preamp circuit using a hoffman AC 30 tone stack. I know that stack is a cathode follower. Well I did not use cathode follower method. I put it passed the coupling cap between the final preamp tube and before PI. Also hoping my work could get checked there.


This was a quick rough draft. There are sure to be slight errors. And in the case of my tone stack and master volume, there could be plenty.


Also, will this 15 watt OT work with my design ( http://www.hammondmfg.com/pdf/EDB1750E.pdf )
This is supposedly the hammond replacement for the Deluxe.

[kagliostro]

If you are thinking to use the 6g3 PA, you are missing the bias Power Supply and the two capacitors between the 220k resistors and the PPIMV potentiometers


as to arrange the PPIMV look to this schematic



The value that I've seen more frequently for the pot of the PPIMV is 1M, may be 500k is fine too


K

[hesamadman]

I dont understand the Bias supply. It travels through the intensity pot of the tremolo 

[HotBluePlates]

One of the things I learned here and from musicians about SE vs PP is the tonality of the amp which is as subjective as politics and religion! but even being sonically challenged, i can hear the difference.

Sure you can. Push-pull cancels even harmonic distortion generated in the output stage.

[kagliostro]

What about to use the AA763 schematic (and layout) discarding the vibrato section and using only the Normal part of the circuit ?

http://el34world.com/charts/Schematics/files/fender/Fender_Deluxe-AA763-schematic.pdf

K

[hesamadman]

What about to use the AA763 schematic (and layout) discarding the vibrato section and using only the Normal part of the circuit ?

http://el34world.com/charts/Schematics/files/fender/Fender_Deluxe-AA763-schematic.pdf

K

So this will be a fixed bias amp, correct?

[kagliostro]

If you look to the catodes of the power tubes and you see they are connected directly to ground or there is only a 1R resistor between the catode and ground, that is near for sure a fixed bias circuit, if you look to those schematic you will find a supply of negative voltage, that is the bias supply


Instead if you see a larger resistor 50R or more, often paralleled by a capacitor, connected between the catodes of the power tubes and ground, that is a catode biased amp


There are also (in some old amp circuit) some examples of mixed bias circuits, but they are difficult to be encountered


K

[hesamadman]

Are you suggesting that I encorporate the bias supply from the schematic you showed, with my schematic? Is the 10kl pot my bias adjustment?

[kagliostro]

As to semplify things my suggestion is you copy the AA763 schematic and layout (only normal chnnel)


then, if you want, you can mod it in the preamp section and add the PPIMV


K

[hesamadman]

Does anyone have an explanation of my current schematic of the 6g3 as to why there does not seem to be a bias adjustment pot? It runs through a 250 kl pot which is the intensity of tremolo. Surely this cant be right as this would adjust the idle plate current as tremolo is adjusted. Im hoping to figure this out before I go and start changing my whole schematic again.

[hesamadman]

If you are thinking to use the 6g3 PA, you are missing the bias Power Supply

I added a bias power supply. I used the one from the AA763 schematic. http://el34world.com/charts/Schematics/files/fender/Fender_Deluxe-AA763-schematic.pdf
I have no idea how this negative voltage supply works. If I understood it a little better maybe I could understand putting it together. I have a few questions regarding,
-Do I use a standard n4007 rectifier diode in this bias circuit
-Do I need the 25uf 50v cap or is it used for tremolo purposes

missing two capacitors between the 220k resistors and the PPIMV potentiometers

I added the .1 caps after my PPIMV. What are the functions of these? I know the ones before are filter caps. Do the ones after make sure the negative voltage does not become affected by grounding through pots?


And I also changed value of my dual volume pot.

If you look to the catodes of the power tubes and you see they are connected directly to ground or there is only a 1R resistor between the catode and ground, that is near for sure a fixed bias circuit, if you look to those schematic you will find a supply of negative voltage, that is the bias supplyInstead if you see a larger resistor 50R or more, often paralleled by a capacitor, connected between the catodes of the power tubes and ground, that is a catode biased amp

This is very useful. Thank you. Im just now diving into power sections. I just added two 1r resistors to cathode of my 6v6's for bias purposes thanks to HBP explaining idle plate current to me the other day.

[kagliostro]

You can use the 1N4007 diode in the bias supply


the 25UF capacitor is part of the bias supply to level the bias voltage, you need it on the circuit


the purpose of the .1 capacitors you added is to avoid the bias voltage rise till Zero volt, if there is no bias voltage your tubes can easily melt


about this capacitor you must double the value of it and double the value of the preceding (.1) cap, this is necessary to preserve the correct


bandwidth to the signal (putting two .1 capacitors in series what you obtain is a .05 cap)


someone recommends to use for the added capacitor a value much more larger than the preceding cap (say 10 times the preceding cap value)


About the value of the PPIMV many guy install an 1M double pot, some a different value, give it a try


K

[hesamadman]

You can use the 1N4007 diode in the bias supply
about this capacitor you must double the value of it and double the value of the preceding (.1) cap, this is necessary to preserve the correct

bandwidth to the signal (putting two .1 capacitors in series what you obtain is a .05 cap)


someone recommends to use for the added capacitor a value much more larger than the preceding cap (say 10 times the preceding cap value)

What if I change the caps before MV to .2 and the ones after to 1uf?

[kagliostro]

If you connect a .2 and a .1 you obtain a .067 cap that acts in the bandwidth in a different way than a .1 cap


to have the same frequency response you must use 2 x .2 cap and you obtain a .1 cap


the fact that the caps are before and after the MV didn't change the fact that they are in series


K

[HotBluePlates]

Does anyone have an explanation of my current schematic of the 6g3 as to why there does not seem to be a bias adjustment pot?

Fender didn't think you needed it. Plenty of non-adjustable fixed-bias amps in the world.

It runs through a 250 kl pot which is the intensity of tremolo. Surely this cant be right as this would adjust the idle plate current as tremolo is adjusted.

You may have moved on away from the 6G3 Deluxe. But here's what you were asking:

Ohm's Law. For your bias voltage to change, there must be a current through the different resistors of the bias supply circuit. If you then vary where on a resistance you look (like the moving wiper on the bias pot) you will see a different voltage dropped across each point along the resistance. Ohm's Law says Volts = Current * Resistance.

Look at the AA763 Deluxe and its bias supply. From the bias tap, there is a rectifier and filter, and then a resistive path to ground for current. The pot just moves to different points along that path to tap-off different bias voltages.

Now look at the 6G3 Deluxe. From the bias tap is a resistor, then a rectifier, then a parallel cap and resistor to ground. That 22kΩ resistor provides the path for current.

Moving left from the top of the filter, passing through the Intensity pot, you come to a cap; that's an open-circuit as far as d.c. is concerned. Move up through the wiper of the Intensity pot, and there is a cap to ground; another open-circuit. Keep moving up to the 220kΩ bias feed resistors. On the other side of them are caps to one side (open-circuit) and tube grids to the other side (also open-circuit).

So the same -26v at the top of the resistor to ground in the bias supply exists at every point along the path from the bias supply to the Intensity pot and to the tubes. With no other voltage level present, there is no direct current through any of these connections, and no voltage is dropped across the Intensity pot.

Now there is an a.c. signal from the tremolo, and that does pass through the caps and cause voltage variations on the Intensity pot. But that's what you want a bias-vary tremolo to do. It just bobbles above/below the mid-point set by the bias supply's -26v.