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Thread: several tranny questions

  1. #1
    Old Timer daz's Avatar
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    several tranny questions

    I cannot for the life of me find specs on the heyboer set in my amp, even the heyboer site doesn't show specs. In fact, they have NOTHING on thier site. Nothing is clickable, just a single page with no info. I built this years ago so i don't know what the tranny specs are. In another thread i said the OT was 8k, but now i see a sticker on it that says "OT 3800". I remember having 2 OT's back then and i wonder if i subbed this at some later date. But as i recall they were both heyboer. Anyways, i cannot find it using any of the numbers on the sticker. I thought it was a heyboer but heyboer's site is worthless. It's one page with nothing clickable. The full sticker on the OT is as follows...

    OT-3800
    HTS-8890
    9960708

    It has only 8 and 16 (yellow and green) ohm taps, not 4. Anyone know what this is and the spec? I thought it was 8k but that sticker makes me think it's 3800 which may be a OT i bought for my peavey classic 30 at the time and i threw it in here. That would speak to it being 3.8k, right? I think it's a heyboeri custom ordered, but again, memory fails me. If so, is this much too low to be using with 6V6? If not, what would the tonal issues be?

    Now the PT.....it IS i believe a regular heyboer and the sticker says...

    PT-290
    9960347

    I only want to know about this one to see if the current would be enough to try 6L6. I suppose it's unlikely but i'd like to try them for the hell of it if possible. I don't know what 6L6's require but till i know what this PT delivers i can't even begin to consider it.

    Anyways, main thing is, do i need to get a new OT since i am running a pair of 6V6, and if so whats out there cheap? I can't afford to be spending right now being out of work so cheap is a necessity. I assume mag comp?

    EDIT: would the 16 ohm be more correct if it's a 3.8k OT ? (do they spec them by the lowest resistance tap?) I read it and it;s double the value of the 8 so am i right that it would be double, 7.6k?

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    Last edited by daz; 10-19-2016 at 04:09 PM.

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    I worked with Heyboer some years ago on a custom OT, and they were friendly and helpful.

    I can't remember the name of the guy I worked with (my memory is getting a bit foggy these days), but I would just call or e-mail them.

    The nice folks at MojoTone in North Carolina could probably also answer your questions, as they work closely with Heyboer.

    Good Luck,

    Ken

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    Old Timer daz's Avatar
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    I guess i will. But as to the OT, after thinking about it i'm almost positive it's 3.8k because i seem to recall that "OT-3800" sticker meaning it's 3.8k and i did order one from them for my classic 30 at the time and put the stock OT back when i sold it. WSoi'm quite sure it' 3.8k. So i figure the 16ohm tap would be double or 7.6k and would be closer to 6V6 impedance. Aren;t they something like 6k optimal? So figuring the 16 ohm pp with my 8 ohm speaker would be more correct i tried it and i like the result. So if someone can confirm this for me, assuming the OT is indeed 3.8k, i'll leave it.

    As to the PT, i only wanted to know whether i can run 6L6 but it's not important so if no one can confirm that PT's current rating i'll just leave the tubes alone and maybe call them at some point to see,. Bu the OT was my main concern.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by daz View Post
    EDIT: would the 16 ohm be more correct if it's a 3.8k OT ? (do they spec them by the lowest resistance tap?) I read it and it;s double the value of the 8 so am i right that it would be double, 7.6k?
    Well, you can't simply connect to a different OT secondary and change the OT primary. It's dependent on the actual load on the secondary to actualize a ratio. You actually have your proposed solution backwards. Connecting the 16 ohm OT secondary to an 8 ohm load will present a 1800 primary to the tubes. If that OT DOES have a 3800 primary into it's rated secondaries you would need to have a 4 ohm secondary connected to an 8 ohm load to present the desired 7600 primary to the power tubes. Or an 8 ohm secondary connected to a 16 ohm speaker load to present a 7600 primary to the tubes. I'll guess you have an 8 ohm load. And you don't have a 4 ohm secondary on that OT. If that's the case then you don't have the means for either configuration. 6L6's would be happy with the 3800 primary so you would observe the OT secondaries as they are.

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    Old Timer daz's Avatar
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    Thats mind numbing to me, but what would using the 16 tap do as far as performance? Would the amp not be as loud or break up earlier or what? I ask because it does sound better on the 16 tap. It even feeds back easier and breaks into a higher harmonic easier. Oh, and i just called them and it is indeed 3.8k and i am using a 8 ohm speaker.

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    Old Timer daz's Avatar
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    Ok, 1800 sounds too far off, i get that now. Should i look for a different OT or is 3800 going to work without compromises tonally?

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    Lifetime Member Enzo's Avatar
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    Although it may be optimized for a certain impedance set, transformers have no inherent impedance, they only have rations. In that, a transformer is like a set of gears. A 10 to 1 gear set will spin the 2nd gear at 10 RPM if you spin 1st gear at 100 RPM. But change teh speed of either one, and it changes the other at the same ration.

    Usually if you are off "one notch" from the specified impedance (ie 4 in the 8 ohm or 8 in the 4 ohm), it works OK and won;t hurt anything.

    Wait, so you are using the 3800 now and it sounds great? Then stop fixing it. It works, sounds even better than whatever else, and as for tonal compromises, you can listen for them. Are there any?

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    Old Timer daz's Avatar
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    I don't know, as i don't have another OT to compare. I like it on the 16 ohm tap tho, possibly better. Warmer, less bright. But i assume thats too low because Chuck said it "presents a 1800 primary to the tubes". The other issue is output power. I assume using the 8 ohm tap will yield more clean power? That would be the deciding factor because while i use it mainly at home, when i DO play with others i don't want to have a hard time getting cleaner tones at stage volume.

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    Lifetime Member Enzo's Avatar
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    So play it at stage volume and see. These are just guitar amps, nothing precision about them. Power is not loudness, so if your 20 watt amp only puts out 17 watts on the wrong tap, you would never hear it in loudness.

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    Old Timer daz's Avatar
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    i know that, but i'm not worried about loudness i'm worried about not being able to get a clean enough tone loud. Thats not to say "a clean sound" at stage volume, i mean a "clean enough" sound at astage volume. I don't expect 2X6V6 to stay real clean at stage volume. But in any case loudness is not my concern. I know it'll get loud enough. Can't test it here.

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  11. #11
    Bent Member Chuck H's Avatar
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    Enzo addressed the 1800 primary by mentioning that being one notch off is usually alright. By one notch he means that you could, for example, run the 8 ohm secondary into a 4 or 16 ohm load. That applies to a properly matched primary though. You don't have a properly matched primary. You have a primary that requires that to properly mate the systems you should be using the secondary tap rated for half your speaker load to present 7600 to the power tubes. So, your 8 and 16 ohm secondary taps are effectively 16 and 32 ohm taps. Right now you are using an 8 ohm load on the NEW 32 ohm tap (formerly your 16 ohm tap remember). That would be two notches off, not one. Your amp probably sounds like it does because the power tubes are working into a much lower than ideal load as if they were partially shorted. Now, if you run your NEW 16 ohm secondary (formerly your 8 ohm secondary remember) into that 8 ohm load you are only one notch off. Which is alright-ish. The tubes are still playing into a load that is lower than ideal, but not harmfully so.

    So use the transformer as marked. That is 8 ohm speaker load on the 8 ohm secondary tap. You will be one notch off ideal. Running a pair of 6V6's into an 1800 primary is asking for it.

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    Old Timer daz's Avatar
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    Thats what i figured from the replies so far, but still have the one question....what would the sonic result be if i got a proper OT ? judging by what i have always heard when running a notch off ideal like a 8 ohm speaker from 16, it usually means a softer tone while ideal is brighter and more articulate/crisp. It's already quite so on 8 so maybe a proper OT would be bright to a fault because i designed the preamp to sound balanced using a softer sounding non ideal OT? I wonder if the ideal OT would allow me to change the pre so it's fuller and more balanced.

    if it would be a good idea, how about this one... http://www.classictone.net/40-18064.html

    I'd like to have the proper primary just for peace of mind, but do 6V6 require 5k or 6.6k to be optimal? I thought i saw 6.6k but not sure.

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    Last edited by daz; 10-19-2016 at 09:36 PM.

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    Old Timer J M Fahey's Avatar
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    Have you ever considered ...... ummmm ..... *measuring* it?

    Instead of all this black candles and chicken blood adivination?

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    Juan Manuel Fahey

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by J M Fahey View Post
    Have you ever considered ...... ummmm ..... *measuring* it?

    Instead of all this black candles and chicken blood adivination?
    umm that would remove all his mystique and drama.

    nosaj

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  15. #15
    Bent Member Chuck H's Avatar
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    Daz, Juan and Jason are just poking you. We've already determined that the current OT is 3800

    The easiest way to find out how the amp performs with a more ideal primary impedance would be to plug the 8 ohm secondary into a 16 ohm load. No need to buy a transformer. You could even just run a 25W 10R resistor in series with the 8 ohm speaker you have to get at least some idea. This also has the benefit of cutting the power to the speaker in half so you can turn it up a little more (for observational purposes ).

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    Quote Originally Posted by daz View Post

    I'd like to have the proper primary just for peace of mind, but do 6V6 require 5k or 6.6k to be optimal? I thought i saw 6.6k but not sure.
    Or we could look at the data sheet: http://www.mif.pg.gda.pl/homepages/f...93/6/6V6GT.pdf Look on page two under "push-pull class AB1" then "Effective Load Resistance". Normally (if there is such a thing) a pair of 6V6s use an 8K P-P load. So using your in-hand OT, if you double the connected load that the tap is rated for, you will get 7.6k, close enough.

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    Turn it up so that everything is louder than everything else.

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    Old Timer daz's Avatar
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    8k? Does this mean 2X6V6 would be 4k? That would put it right where my OT is, yes?

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    Quote Originally Posted by daz View Post
    8k? Does this mean 2X6V6 would be 4k? That would put it right where my OT is, yes?
    No, when you look on the data sheet under "Push-Pull Class AB1", I abbreviated this. In addition notice it says "for two tubes" So by looking there you have already determined that you have two tubes in total and the load is 8k Plate to Plate, one tube per leg; one push, one pull.

    If you had two 6V6s PER OUTPUT LEG in parallel, then you would cut the value in half and have 4k P-P. Another way to say this is to say you have four 6V6s in total.

    Just to be sure, you do have two tubes total? If so, then the data sheet says 8K. But as we have determined before, most times a one degree mismatch is OK. I have heard Marshalls don't like this but I can't speak personally about this.

    So we are back to using a 16 ohm speaker since you have an 8 and 16 ohm tap. You need to double the connected load to get 7.6k reflected back to the primary. So as Chuck stated in post #11, you really have a 16 and 32 ohm tap since your primary is 3.8k and not 8k. You only have half the required data sheet value with your 3.8k.

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    Turn it up so that everything is louder than everything else.

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    Old Timer daz's Avatar
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    Yes, 2X6V6 and a 8 ohm speaker. Then i take it i would be well advised to get a more proper OT, and if so how far off from a 8k primary can go with no observable tonal/volume difference from 8k? I linked a classictone 6.6k OT above, (post #12) would that be a good choice?

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  20. #20
    Bent Member Chuck H's Avatar
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    Or...

    You could get another speaker! Probably a little more expensive, but what will prove more useful in your future, another OT or another speaker?

    There's no dramatic issue using the OT you have. In fact, you can plug it into 4x12 Marshall cab now and be at the correct impedance

    Do you have a high-ish watt 10R resistor? Even a 10W at anything between, say, 6R to 12R would do. You'd need to mentally account for the amp being a little lower in output power, but you could get an idea of how the "proper" impedance "feels".

    On the subject of proper impedance... The actual ideal impedance is a bit of a misnomer. There will be an ideal impedance for maximum output power and an ideal impedance for minimum distortion. The data sheets don't specify the criteria (but they do show a distortion figure). The two criteria won't produce the same primary impedance. Another view might be that a compromise impedance is ideal. One that has the greatest amount of power for distortion ratio. So that's three possible "ideal" impedance numbers. And they will all depend on your specific tubes, your plate voltage and somewhat on your bias and the dynamic character of your load. In other words... Close is fine and the actual difference between ideal and close is very small. That's why Fender amps have an extension speaker jack that's simply paralleled with the stock load. Doing so with a Fender amp renders it in the same operating conditions as what you are doing now. It's ok, really! But if you MUST hear it, buy a resistor first instead of an OT before spending on an OT. On that matter...

    Shipping charges have become pretty stupid. OT's are heavy. If you MUST buy an OT, look up the shipping charge too because it's going to be a considerable percentage of your purchase.

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    Quote Originally Posted by daz View Post
    Yes, 2X6V6 and a 8 ohm speaker. Then i take it i would be well advised to get a more proper OT, and if so how far off from a 8k primary can go with no observable tonal/volume difference from 8k? I linked a classictone 6.6k OT above, (post #12) would that be a good choice?
    Sorry, I forgot to look at that link as I was going to respond to it. Trainwreck amps use this 6.6k OTs because it can run 6V6s and EL34s. That 6.6k impedance value is halfway between the 3.4-4k for the EL34s and the 8K for the 6V6s, so it works for both since it's only a half step mismatch. So yes go ahead and use that 6.6k for your pair of 6V6s. And I like that it has the multi-tap secondary for other speaker options for later. Also, since it has a 30 watt rating, it will have a good amount of iron for the lower output of a pair of 6V6s and give you good bass response.

    EDIT: Simulpost with Chuck. Great info there. I just wanted to show the data sheet info way to find the value. Then things can be adjusted as Chuck outlined. That's why this is such an open subject. There's many ways to make things work and much of the time it's "close enough for rock & roll."

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    Old Timer daz's Avatar
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    Well, i'll look at graigs list and see if there are any 16 ohm speakers i might wanna try. Only thing is unless i can find the same model i'm using used/broken in, it's be hard to tell what is making for the difference i hear. As to load resistors, i have some aluminum chassis mounts but i'll have to see if any fall within 6 to 12 ohms. But that would be series your talking about to get 16 ohms....won't series resistance affect the tone a lot? Anyways i'll see what i have.

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    Quote Originally Posted by daz View Post
    Yes, 2X6V6 and a 8 ohm speaker. ... how far off from a 8k primary can go with no observable tonal/volume difference from 8k?
    Yeouch!!

    This is a large, economy size can of worms.

    Back in the Golden Age, the tube designer-guys would design a new tube. They'd then go tinker with the thing so as to find out what the best OT ratio was for it (them?). They would set up a series of "victim" amplifiers and go tinker with loads and then measure things.

    It turns out that for every tube, there is a maximum-power loading for a given amplifier setup (i.e. class AB, etc.) If you have, for instance, a pair of 6L6s, the max-power point is near 4000 to 4400 ohms plate to plate. They would then go test the distortion and look at how distortion varied with loading. No surprise, they found that there was a place where the sum of second harmonic and third harmonic (those being the biggest contributors) was a minimum. For the 6L6, this is something like 6K to 6.6K.

    So the hifi guys would go load them at 6K-ish for low distortion. The guitar amp guys would fight over power claims, so they'd load them at 4K-ish for better advertising.

    Both curves are very, very broad. There is no sharp peak of power at the supposed perfect loading, and no sharp minimum of distortion at the supposed ideal load. But they are differences. It's really, really hard to say how far away from either optimum, or just any other loading point you can go without an observable tone or volume difference. As you know, even very slight tone and volume differences can get noticed.

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    Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

    Oh, wait! That sounds familiar, somehow.

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    Old Timer daz's Avatar
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    ok, so i have more info that will fit into my tiny brain already and it just keeps coming making for more confusion. So let me make this easy.....is my 3.8k OT using the 8 ohm tap with my 8 ohm speaker with two 6V6's pushing things too far in one direction or another ***based on general consensus*** as you see it, that i would be better off getting a 16 ohm speaker or a new OT? And if i get a new OT what spec would definitely be agreed upon by all. I appreciate all the replies, i really do. But so many things have been said I'm really not sure what the safest bet is. To maybe make it easier to answer, i want enough clean headroom to use it in a band situation for typical small to medium bar levels and have a somewhat clean sound when i roll the guitar back. On the other hand if it's loud and clean as can be, maybe too optimal a spec would be too bright and harsh so maybe consider that.

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  25. #25
    Bent Member Chuck H's Avatar
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    OT at 6.6k for max power. That number will vary with your specific plate voltage, etc. but since you won't find a 6k or 6.8k transformer the 6.6k "standard" value will have to do. That max power thing DOES make a concession for distortion figure BUT THAT IS FOR HI FI!!! For a guitar amp it's the little harmonic anomalies that make the difference between a workman like tone and a more musically expressive tone. We're not talking about clipping distortion here. The stuff that guitar players associate with "clean" vs. "distorted". We're talking about insinuated harmonics. Like the root tone has a (very slightly) increased ratio of the third harmonic in the content of the final output. This would be measured in percentages in the few, or even decimals. The greatest output is the typical choice for guitar amps, so... This is the sound that our ears have become acclimated to and the sound that guitar pickups have been designed to work with and the sound that studios expect and the sound that sound engineers monitoring stages have become familiar with... Get what I'm sayin'??? If you consciously veer from the norm you'll be into less explored and less accessible territory. So... 6.6k

    Yet you like the tone at 1.8k primary!!! This is where tone becomes subjective. You absolutely WILL hear and feel the tone move further to one direction as you go from 1800 to 3800 to 7600 (or 6600). In this light 6600 goes further away from the tone you already preferred! Now, 1800 is an unreasonable load for a pair of 6V6's. Just play the rig at 3800 primary, which is reasonable, and be happy.

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    Old Timer daz's Avatar
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    Will do Chuck. Thats sounded reaffirming enough for me. It does sound great so i'll just leave it. I just can't leave something alone if i'm unsure whether it could be robbing tone or in this case volume and tone. But i just ran it w/o the delay in the loop and it gets freakin loud and cleans up well. It won't get loud enough to gig with the delay (it starts blocking in the DSP well before loud) tho so i gotta get that loop working. On that note Chuck, can you think of a amp similar to mine with a single AX7 powered loop that would work where you put the SS loop into my schematic? Gotta be before the master so that would be the only place i can imagine.

    By the way, i just noticed the name of the jpg you posted of my schematic with your loop idea and i actually laughed out loud !

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    Quote Originally Posted by Chuck H View Post
    Just play the rig at 3800 primary, which is reasonable, and be happy.
    If it's loud and clean enough I'd run it like Chuck says. Anyway the speaker impedance is only 8ohms over a narrow band of frequencies. It will be greater than 8ohms above and below that so the 6V6s will also see an impedance greater than 3800 for higher and lower frequencies (see graph below)

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    Bent Member Chuck H's Avatar
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    Indeed!

    I test a little peripheral stuff whenever I have an amp on the bench and I'm often surprised at how little difference a 100% mismatch makes in output power with an actual speaker load. Usually it'll be virtually NO difference or a small increase mismatching down and only a few percent loss mismatching up. An interesting observation is that with a resistive load there is sometimes more power with a 100% mismatch up and a few percent loss mismatching down.?. I speculate this is because the white coats that designed the tube, transformer and speaker relationships long ago were paying attention to the fact that an actual loud speaker presents a higher average impedance at frequency than a resistive load, so, the efficient ratios we mimic today are grandfathered in. Testing with a purely resistive load is more about detecting operational faults than actual musical performance. The fact that RMS watts are standardized from a resistive load not withstanding.

    So, daz, in my humble observation you may be getting more power with the 3800 primary than you would with a "proper" 6600 primary when connected to an actual speaker (at some relative increase in harmonic distortion).

    EDIT: Hey daz, for more peace of mind consider that a very popular Marshall mod is to swap the el34's for 6V6's for. Typical primary impedance in these Marshall's is pretty much right where you're amp is.

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