no frills cheap PT

[lowell]

I need the smallest and cheapest PT possible with these ratings. Please advise if have any recommendations.

120v primary
300-0-300 secondary
6.3v secondary
VA of around 10

Am using ss rectifier, 1 12ax7, 1 6V6.

thanks in advance

[redelephant]

Have u checked EDCOR?
www.edcorusa.com

[EFK]

Edcor has some surprisingly good stuff! Looks pretty too. Also, if you call Heyboer and tell them what you want, they almost assuredly have specs for something just like it.

[lowell]

Edcor looks great. They have one that fits my specs quite well. The XPWR158-120/240.

[Wilder Amplification]

I need the smallest and cheapest PT possible with these ratings. Please advise if have any recommendations.

120v primary
300-0-300 secondary
6.3v secondary
VA of around 10

Am using ss rectifier, 1 12ax7, 1 6V6.

thanks in advance

I'd seriously rethink that VA rating. 6.3 of that is for heater power alone. Throw in the peak power on top of that and a VA of 10 simply won't cut it.

How much output power are you seeking?

[loudthud]

If you are a little flexable on the voltage, look here:

Allied Electronics - Catalog

[lowell]

6v6
If=.5a
Vf=6.3v
Pf=.5x6.3=3.15watts

12ax7
If=.150a (per half of tube)
Vf=6.3v
Pf=.3x6.3=1.9watts

12ax7 Wa is apprx 2watts total for both stages
6v6 Wa is apprx 8watts (using resistive load - no OT)

So yeah I guess you're right. Add on some wattage from bleeder resistors, pilot light etc... and it looks like more of an 18watt application.

[lowell]

Yes! Nice LT. That's more in my price range. The 6K3VG is the one.

[greekie]

... and add some watts for the very bad efficiency of the circuits we are using!

A 6V6 in single-ended operation draws 47mA to the a node at and 7mA at the screen-grid at 250V for 4,5W operation. That's 0,047+0,007 * 250 = 13,5W for that tube alone. Then you have the heaters which are ~6W, so now we're up around 20VA. Then we have the power circuitry as you mention, etc.

Most Champ transformers I see are around 40-60VA. I built an amp for a kid with a PL84 tube and a 12AX7 tube. We used an old transformer from the little Marshall transistor combo that was the donor chassis. It was rated 40VA and supplied the heaters as well as power to a back to back 30VA transformer that supplied the high voltage. Both those transformers got not-hot-but-a-bit-warm when the amp had been playing for some time.

Jake

[lowell]

Right on Jake thanks for the info... you're right.

[greekie]

Not to sound grumpy or anything, but my usual experience is that what you can save now by cheaping out, will bite you in the *$$ later!

When I build for customers I always plan the budget, so I can do stuff right. If that means that the prices of my amps aren't competitive with Bugera or Peavey - fine, buy one of those! I'd rather build stuff that I can still be proud of ten years down the line, than stuff that'll come back and bite me because of repairs, etc. One of my selling points is a 5 yr warranty on everything but tubes, fuses and filter caps. And so far, I've only had to do replacements 5 times on 200+ amps in the last 10 years. All due to component failure, one time a transformer which I had calculated was up to the job. What I didn't calculate, was my vendor sending me the wrong model, and me not noticing. So that got replaced by the vendor, due to the pretty strict laws here in Denmark when it comes to warranty and returns.

I used to cheap out on my own stuff. But as usual, that came back and bit me! So now, instead of building myself "something" now, I'll rather plan for "the thing" later.

That little amp it playing happy till this day (2 yrs now, played by that kid every day!) and the three Telefunken PL84 I pulled from an old TV I found in a dumpster is still in his arsenal, with the old one not even being worn down yet! The PL84 is actually an interesting tube. Besides it's 15V heater, it's like an EL83 - really cool for small amps.

YMMV.

Jake

[lowell]

I hear ya Jake. I also feel that transformers are very overhyped. I'm also after guitar tone, not hi-fi tone so all this "what is the BEST transformer" crap is ridiculous in my opinion. It's not that I don't feel a transformer is an important part of the tone of an amp... it is! But for guitar it's not so critical in my opinion and for my taste. Really I feel that if you're after an old grainy overdrive tone, then a cheaper or less quality transformer may be the right ticket! Transformers are another tonal element, I don't think that brand name should be what one goes by.

[greekie]

I agree with you. It is definitely not about the brand of transformer!

However, we should try to think about the PT and OT, not as "black boxes", but as elements that do something to our sound. If our power section is high impedance, and therefore sags a lot during load, that might be just what we are after! A larger PT from some well known brand will not make it sound "better", if what we are after is the sound that we get from that high impedance power supply! In the same way, the OT we like might shunt certain frequencies, or saturate at a given volume - a bigger one will again not make that "better", if that isn't what we want.

IMHO, I don't care about brands, as long as the quality is good!

Jake

[jimboyogi]

Not quite 300-ct-300, but pretty close, with 50VA -

Antek - AN-05T280

[lowell]

Is that close? Not sure but think I can only get about 1.3 of half of that 290 (145) once rectified. ??