Power Transformer

[FunkyE9th]

I'm thinking of getting the attached PT for my 2nd build.

If I'm understanding the spec correctly, I will get 325-0-325 (650V) if I draw 70mA. What I'm concerned with is I do not know what the max current is that I can draw. Is 70mA the max? If I draw more than 70ma, will I fry the PT? Or will it still work, but just sag below the specified voltage?

Thanks,

-FunkyE9th

[Phil_S]

I think that I've posted on this topic here before, in detail. You need to hang a rectifier and a load on it, and test it. See if you can find what I wrote before. If you can't PM me and I'll see if I can find it.

[FunkyE9th]

I don't have the PT for me to load. I was hoping that before I buy it, I can find out its max capabilities. It's typical for electronic parts to be spec'd for max/min. I'm trying to understand if a PT as spec'd as shown in the attachment, if those are max characteristics of the PT.

[Phil_S]

Sorry, I misunderstood. It appears that it's limit is 70ma. You are likely to overload it beyond that, meaning it is unlikely to hold up under the load. If you need more than 70mA for your circuit, this is the wrong PT.

For example, a pair of EL84, PP, cathode biased, requires 72-92 mA for plates + 8-22 mA for the screens. To be safe, you need capacity in excess of 92+22, because you need to allow for the preamp draw, as well. 120mA would be on the edge for 3*12AX7 + 2*EL84 with solid state rectifier.

Also, consider that a PT has a VA rating on the primary. This rating is for all secondary winding together, including filaments, which have considerable current draw.

I would only buy this PT for building a single ended, one power tube amp.

Really, though, Musical Power Supplies has a 325-0-325 at 120mA (I think) for a price that can't be beat. Why fool around with uncertainty?

[FunkyE9th]

AES has the part listed for a Tweed Deluxe, so it tends to imply that it can take 2 6v6s, but 70mA seemed low to me, so I posted my question here. I was thinking of using it for a Dual SE Amp. Anyway, I ended up ordering a Weber...same PT I ordered before.

[Andy Le Blanc]

I moded an old champ replacing the rectifier with another power tube
and replaced the SE tranny with a P-P etc........ the PT is the same as a princeton
so figured it would go with a pair 6v6...... the OPT was scrounged from an old
hifi and was close enough but..... the loading drew more current than the
PT could supply..... it sounded great...... on the bench...... but didnt make
a lot of watts when pushed....... gut less.... very dissapointing.....

checkout the OPT , tube type, and loading that it was designed around
see if your application your designing for is in the same ballpark
otherwise add up the draw as Phil_s suggests

[Phil_S]

I'm no expert, but my reading of the tube data sheet suggests you need about 75ma for a pair of 6V6GT (plate+screen) and I'd add maybe 5-10mA for the preamp tubes. 90mA seems like an appropriate and conservative rating for a Deluxe. However, voltage plays a big part in the equation. As voltage rises, you need less mA. It is quite possible that 70mA will do the job. While I'd guess a 70mA PT would run on the hot side, we should consider that Leo Fender was a businessman who had a reputation for cutting cost at every opportunity. It's quite possible it would run just fine in that application. I don't mean to be seen as speaking with a forked tongue, but the new information informs the answer a bit differently. Anyway, the Weber PT is a good deal. Good luck.

[FunkyE9th]

Phil,

I agree with your numbers. I already have a DualSE amp that I built using 2 6v6s with Weber PT. It was drawing ~40mA each, that includes screen current, so actual plate current should be a little less than that. That's why I was surprised that the AES PT was advertised for a tweed deluxe (it's also advertised for champ and princeton). Since I was ordering most of my parts from AES, except for the PT, I thought it might be a good idea to consider their PT...getting everything from one place would simplify things.

-FunkyE9th

[sportster4eva]

I have used that transformer in a tweed Deluxe, but it isn't really up to it. It will run a tweed Princeton or a Champ ok, but that's about it. In fact, it's actually too small for the mounting holes in a Deluxe chassis. The one I use in all my deluxe builds is the P-TF41316. It's good for blackface Deluxes and Princetons too. It drops right in, and gives you about 390v loaded using a 5y3 recto.