Stancor transformer

[johnnyreece]

A 5U4GB requires about 50% more filament current than a GZ34, so be careful you don't toast your PT.

[Eric_BK]

Thanks for all of the info, guys. After careful consideration, I am ditching the SR idea and going for the JTM 45 build. I figure if I'm going to be installing KT88s in the amp, I may as well go all out with a decent Marshall style. The OT specs show that it only has 8 and 16 ohm taps, which shouldn't be a problem. If it is, I'll just pick up a new OT, as I'm getting a choke anyway.

[Eric_BK]

And also sticking with the GZ34

[Phil_S]

Read your PT spec posted earlier in the thread. It specifies the limit of 5V current.

[Eric_BK]

Checking specs now.

[Eric_BK]

The GZ34 handles 5v, according to the JJ specs. Is that going to be an issue with this?

[Eric_BK]

I mean, the amp this was in previously had a GZ34 in it. I'm thinking it shouldn't be a problem.

[Phil_S]

OK, you looked but not at the correct thing. I understand that you are still learning. Words are important. Current = Amps. We know that PT has a 5V winding. The question you should answer for yourself is whether you have a choice of rectifiers, as one needs 1.9A and the other needs 3.0A. You know which needs what by looking at the chart I posted or at the tube spec sheets, for which I posted a link.

[Eric_BK]

Based on this document, it seems like a safe bet that the 5U4G or the GZ34 would be ideal. I'm still researching but, I feel that there's a solid foundation for the amp.

The document details the specs and usage for the PT and OT I have.


http://www.tubebooks.org/file_downloads ... matics.pdf

[Phil_S]

Good progress!

[Eric_BK]

Ok, I found this bad boy at Tube Depot. The specs say it will drop the B+ voltage by 30 - 40 volts.

[Phil_S]

I can see you are trying hard. It is important to look at more than one parameter. Voltage drop is just one thing.

I think you are confused. A 5R4 will drop 67V at 250mA. That is the tube spec. Every tube rectifier is spec'd in this manner. Some drop more than others. Look up the tube spec. When you do, you'll find that the limit for the first filter cap is 4mf. That isn't much filtering, so this tube may not be so well suited to a guitar amp.

You have to know the load in mA then estimate the drop. Your PT supplies 400-0-400 to the rectifier. A JTM45 will require about 200mA which is the limit of your particular PT. Yes, that bad boy will probably give you the most voltage drop. I'm guessing you'll end up right around 500V. You'd probably do better with a different rectifier and choke input.

[Eric_BK]

I picked up a choke - Hammond 194G. It's installed. I swear, if this amp works, I'm naming it Phil.

[Phil_S]

Well, you got a good second opinion over at AX84 and he's more articulate that I am. Knows more, too. I think with choke input, solid state rectifier, you are looking at plate voltage of about 370. (Rule of thumb: Secondary VAC/2.2; guessing you get 820/2.2=373VDC.) This is a nice spot for lots of amps and you'll have plenty of plate current on tap.

IMO, you should skip the tube rectifier, as voltage will be even lower and that is probably lower than you want to go plus you are limited to those that can manage >200mA. Save your money and the effort. Solid state diodes are 10¢ each. If you don't like it, you can always use a tube.

And please call it anything but Phil!

[Structo]

Thanks for that spec sheet.

Some neat ideas there.