Need help replacing a broken transformer

[docSanchez]

Hello

I have been trying to fix up my Ashdown Five-Fifteen solid state 100-watt bass amp, but two of the solder lugs ripped out of the transformer at some point. I know I need to get a new one, but I am very inexperienced with transformers and wanted some help making sure I would purchase the correct transformer.

The tech-support at Ashdown told me that the "transformer is a 100VA unit with one centre tapped secondary ( 31 - 0 - 31 volts )"

On the unit itself it says:

120V - 100V - Fuse
YW PT-FIVE FIFTEEN-100/120V
31V - 0 - 31V

and it has six terminals, though the center bottom terminal isn't used.

However, all the transformers I looked at have only 5 terminals:

These are the transformers I found:
Hammond 166E30 166E30 Hammond Manufacturing Transformers
Hammond 166F30 166F30 Hammond Manufacturing Transformers
Hammond 166G30 166G30 Hammond Manufacturing Transformers

I can't tell the difference between any of them except size. There's also this one:
Hammond 165530 http://www.alliedelec.com/search/pro...6250#tab=Specs
Which is more expensive...also it says dual bobbin and I think the amp tech would have mentioned that (also if that means what I think it means, the transformer I have is not dual bobbin)

Can anybody help me select the one I need?

[Enzo]

The transformer in there now uses five terminals. The transformers you can find have five terminals.

The old one has an extra terminal for use on 100v power systems like in Japan.

100VA means essentially 100 watts. Watts is volts times amps - so VA. And at 30v, that is a little over 3A.

The three Hammond types are way too small. The difference is in size, yes, and you have to be aware of the room inside the amp. No point in buying a transformer that is 5" tall if the amp chassis is only 4" tall.

But those transformers vary in size because their current ratings also vary.

The Allied one has plenty of current - it is a 300VA transformer, but it is 30v CT. CT means center tapped, and 30vCT is the same as 15-0-15. Your 31-0-31 is the same as 62v CT.

Dual bobbin doesn't matter to you. It refers to how the thing is constructed.

[docSanchez]

Would this be closer to what I need?
Hammond Manufacturing - 186F56 - Power Products - Transformers - Allied Electronics

It's only 56v CT but am I at least heading in the right direction?

Or this?
http://www.mouser.com/ProductDetail/...tM3For1gnEA%3d

[Enzo]

The Hammond would probably work, but the amp would not put out full power. The Allied part is back to 36v CT, which is 18-0-18.

Is the original a toroid?

[olddawg]

Have you tried to fix the old transformer? What do you mean by broken lugs? If you can get to the winding connections you can scrape the lacquer off of the ends of the broken winding wires and attach new lugs. Sometimes you need to solder a small length of wire with some shrink wrap to reach. If you have access to the windings at all, with a little patience it should be repairable. Sometimes you have to cut some paper off to get to the windings. But if the PT is open anyway, what have you got to lose?

[docSanchez]

Ok. That might be acceptable... I'll keep looking though.
And I do not know if it is a toroid, but I don't think so. It looks like those dual bobbin transformers, without the split in between.

[docSanchez]

See, there were no winding wires. Just 6 lugs sticking out of the transformer. I'll see what I can do to get access to the windings. You're right, it's shot anyways, might as well give it a go!

[Enzo]

OK, not a toroid then.

SInce the transformer is already about to be replaced, you are at the what is there to lose stage. WHere the terminals come out, inside ther are wires attached to them. You wil have to carefully cut away some of the paper or tape that covers the windings to get at it.

[docSanchez]

No luck. Spent almost two weeks messing with the terminals and the combinations and I just need a new transformer.
Also, I need the schematic for the amp, so I know how to wire the transformer. At this point I almost feel like it makes more sense to just sell it as a 1x15 bass cab.

[Enzo]

How to wire it? As described, the transformer has a primary, and a center tapped single secondary. The primary gets wired up to the mains, and the secondary center tap goes to ground, and the two hots go to the rectifiers.

[J M Fahey]

Hi docs.
That transformer *was* previously wired to the board or rectifiers and to mains.
Did you make a sketch of that ... or took a picture?
Worst case, post a couple pictures of where you think it was previously connected and we may guess.
PS: if you find nothing closer, that 56V 100VA will do.
Your amp will put out *slightly* less power, I doubt you will notice it.

[docSanchez]

I'm hitting myself in the head for not taking pictures: I had originally labeled all the wires with tape but took them all off after I thought I had solved the problem (fixing the power transistors) earlier on. I'm just going to go with the lower power transformer and call it good. Hopefully it will also be less likely to blow with less juice running through it.

As for the connections, I just wondered if polarity mattered. I know where to plug everything in: I just don't know if I need to be polarity aware. but of course, if I do need to mind to polarity, I can just wire it up one way; fuse blows I just switch it. (I'm talking about the primary terminals)

[Enzo]

It is AC, it has no polarity.

If you wire two windings together, then you must concern yourself with keeping them in phase. That is not your center tap, I refer to something like a dual primary and wiring it series or parallel.

[docSanchez]

D-oh! I feel quite ridiculous now :P Well, I'll order the new transformer this weekend and see what happens next week.