5F6-A PT choice ?

[worth]

Kevin Oconner recommends using the Hammond 272JX PT rated at 300-0-300@250ma for a 5F6-A build. Any thoughts on this ? Agree.. disagree ?

[FYL]

Some of KOC's recommendations seem to be based on sponsorships from Hammond and Plitron... The 300V 272JX is OK but B+ will be on the low side: the original 8087 used by Fender was a 325V model.

[worth]

Right... but won't the B+ rise quite a bit if the PT is rated at 250ma. , and the circuit is pulling pulling less than 200ma. ? I've got a Hammond 272HX rated at 300-0-300@200ma. in a 2-6L6 , 5AR4, 2-12AX7 circuit , that measures 325V before the rectifer.

[dynaman1]

Use what you have. That's the cheapest option!

FWIW, I used Doug's PT and it worked fine - voltages were right on.

[FYL]

Right... but won't the B+ rise quite a bit if the PT is rated at 250ma. , and the circuit is pulling pulling less than 200ma. ? I've got a Hammond 272HX rated at 300-0-300@200ma. in a 2-6L6 , 5AR4, 2-12AX7 circuit , that measures 325V before the rectifer.

B+ will be higher with lower loads, but what you've measured could very well be caused by high mains: most Hammond PTs were designed for 110 V mains (they now target a more realistic 120 V). Check the date code on the label: if the OT is from 2009 or older, it's a 110 V model.

[phsyconoodler]

Hammond makes a replacement PT for the bassman that works just fine.The lower voltage from the 272JX will be just fine too.It makes the amp less trebly overall,just not exactly like an original.The 272JX is a fine transformer but I would use the right one to get the right tone.

The hammond is a 290DX and it has a 650v CT primary. 325-0-325. Perfect.

[worth]

I posted about 2 weeks ago because the 290DX I bought from Antique Electronics actually mea sured 352-0-352 ... not 325-0-325 as advertised. I've sent the transformer back. I really want to find a PT that is REALLY 325-0-325@200ma.

[FYL]

Here are the Hammond specs: http://www.hammondmfg.com/pdf/EDB290DX.pdf

Getting 350 V would mean that you've measured an unloaded PT using 115 V mains.

[worth]

Nope.. measured at 120V AC , loaded with 2X6L6 , 1X 5AR4 , and 4X12AX7. I'm well aware of the 290DX specs , and have been talking to Antique Electronics about the problem.

[mresistor]

What about Allens TP40?

[FYL]

Nope.. measured at 120V AC , loaded with 2X6L6 , 1X 5AR4 , and 4X12AX7.

Quite strange, Hammond is usually spot-on.

[worth]

Right.. they ARE usually spot on. I've bought two Hammond "Fender" power transformers in the last year , ( Deluxe Reverb, and Showman replacements )... both had correct voltages. I really don't see why this transformer is advertised as a replacement for a Bandmaster ( 325-0-325 ), Super Reverb (360-0-360), Tweed Bassman (325-0-325), and the Vibroverb (355-0-355 ). If I order a 325-0-325 PT , and receive a 360-0-360 , or vice-verse , I would be very unhappy about it.

[Tiny_Daddy]

One thing to note here: If you buy a guitar amp replacement transformer, it is application-specific and should measure correctly when installed in the correct guitar amp. But other transformers are rated for a particular voltage at a particular RESTIVE load. For example a rating of 350V at 200mA means the transformer was tested with a 1750 ohms load that drags the voltage down to 350V. Smaller loads (higher resistance) will allow more voltage. Since our amps use a rectifier/capacitor and do not draw full power unless played loud, estimating the B+ becomes complex. That's why I stick with guitar amp replacement transformers where possible.

[bigdaddy]

If you want  PT that is as close to exact as can be go for the extra money and buy a Mercury Magnetics. Whether they are what they say is debatable but I have had some great sounding amps using them.

Those other PTs are generic and can be used for many different uses. The funny thing is that if you have worked on Fender amps from many different eras you'll find many different PTs especially when Leo ran the show. He used what he had and could get.

So IMO it's not about being correct, what is correct? It's about the end game and how the amp will sound. Amps with overbuilt PTs sound different then ones with a PT working close to it's maximum and as for voltage again it's preference, they will sound different with different voltages. You should ask yourself what you want the amp's tone characteristics to be when you decide on any component.

[worth]

You're right.. and I DO know what tone I'm after. That's why I ordered the 290DX rated at 325-0-325@200ma., then found it was 27V higher. I understand that Fender's ratings were +/- 20% , but today in 2010 , when Hammond goes to the trouble to publish their ratings taken at 120V, and I power up the LOADED amp at 120v , I expect it to be very close to Hammonds ratings. Now , if Hammond had said something like , " the 290DX is somewhere between 325v and 360v " then I would'nt have a complaint.. I would just use a different rectifier or a Zener to get the voltage where I want it. But then again , I probably wouldn't buy a new PT without knowing exactly where the voltages are going to be.

[phsyconoodler]

27v is nothing to a tube amp.Adjust the bias and get on with your build

[worth]

That's really odd... you just said that you should "use the right transformer to get the right tone." Aren't you talking about voltage ? Anyway.. my original point was that I'm looking for a PT that will deliver 325-0-325@200ma at 120V.

[phsyconoodler]

Ok,I have used the Hammond PT and it did indeed deliver the correct voltages at 117v wall voltage at the time of measurement.

  I have also went between three meters and found different readings.I calibrate my meters and use fresh batteries before I get all bent out of shape about differences.
   I have a high quality meter I use at work that is easy to calibrate and I use that as my standard.I use Fluke meters mostly at home,having good luck with them.I do not use cheap meters and expect repeatable,accurate results.
  That may be one reason why some readings are not where we think they should be.Not saying that's your issue,but I have only had one Hammond PT issue in the last 6 years,and it was not an inaccurate voltage reading.
  You can call Hammond and ask if you are in doubt,they will let you talk to technical support staff.
   

[bigdaddy]

I agree with you Tennessee, you had every right to send back that tranny. You are correct to want what you want and to get what you pay for. Also as far as I know isn't there like a +/- 20% even on trannys?

I'm a little dubious about Hammond these days. So far me and another builder here totally burnt out the same model new Hammond PT building a firefly. What we both did should NOT have done that. They changed their transformers and the specs.

[phsyconoodler]

Yes I do agree they are not as good as the classic tube series has been in the past for me.
  The one failure I had was a short to the transformer housing in an 'upgrade' Princeton Reverb PT.It shocked me when I touched the chassis!They replaced it immediately with zero hassle and they paid the shipping.Which makes me wonder if they have had some quality control issues.A hi-pot tested tranny should never make it in the hands of a builder if it's no good.

  That being said,I have used many PT's before and since that incident with Zero complaints.

[bluesbear]

I always err on the low side. Easier on the tubes and I get a smoother, more violin-like tone as apposed to a bright, piano-like tone with higher voltages. Both are fine; I just prefer it that way.
Dave

[Tiny_Daddy]

I also err on the low side to avoid the surprise of having too much voltage for the filter caps.

[LooseChange]

Me too.  Low side and below 450v B+ so I can use easily attainable 450v filter caps.

[BarryW]

I've got a spare Allen TP40 if you can use it

[worth]

Thanks Barry.. I ordered one at 9:00 this morning. I know what I'm paying for when I buy from David Allen.. he answers questions  , even if you don't buy his parts.