several tranny questions

[daz]

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?

[Ken Moon]

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

[daz]

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.

[Chuck H]

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.

[daz]

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.

[daz]

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?

[Enzo]

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?

[daz]

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.

[Enzo]

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.

[daz]

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.

[Chuck H]

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.

[daz]

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.

[J M Fahey]

Have you ever considered ...... ummmm ..... *measuring* it?

Instead of all this black candles and chicken blood adivination?

[nosaj]

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

[Chuck H]

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 ).