hammond 374bx

[leo450450]

Hi guys; my 1st post!

I have this Hammond power transformer 373BX (750volt @200mA secondary) that was used in a ampeg b15.

I'm wondering if/where I can use it in another build where the specs are not exactly as specified.

In other words, how much can I vary the voltage/amperage without blowing things up?

thanks

Leo

[wpaulvogel]

This is a very general question. The transformer unloaded produces nearly 400-0-400. 397-0-397. It’s spec is 375-0-375 @ 200mA draw so it’s stout. It’ll make well over useable voltage for current production EL34’s and 6L6GC. KT88’s or 6550’s would live well and be quite a nice probably 75 watt amp with a 1.75k output transformer. Yes you could use a 5U4GB rectifier to drop some voltage but what’s the fun in that. I wouldn’t band aid the situation. The 300 series Hammond transformers are built like tanks and I’d take advantage of the ruggedness. Would you like to sell it to get something more suited for your application?

[pdf64]

With the likely 500V HT, wouldn’t a 1k75 OT result in the 200mA rating being significantly exceeded at high output?

[Stevem]

That must be a power transformer for a late B15 / B18model when they where 60 watts in output because the earlier 30 watt ones like mine do not need 200 ma.

[Guy77]

I have used the 273bx (700vct) on several builds with the 115v tap . These were 50 watt amps (2x6L6) that had 3 - 5 preamp tubes. My B+ ran at 433v with a 120v wall voltage and my heaters were spot on 3.15v.
Just to give you a reference on the types of voltages you can get.


Cheers

Guy

[Phil_S]

The question is fuzzy, "...without blowing things up?" If you load the PT with a circuit similar to the one it powered, then there isn't much risk. If your question really is about how to drop voltage for another kind of amp, then the answer I'd suggest is to use a full wave rectifier with choke input. The choke needs to be stout enough to carry current for the whole circuit. This is different from the chokes we sometimes see between the plate and screen nodes. With FW choke input, this PT should output B+ in the low 300's; I'd guess around 330-340. This will be usable with a variety of tubes that you wouldn't be able to use otherwise.

As another answer says, depending on what you really want to do, it might be better to sell this PT and get what you really want or need. This is a hefty PT and it is likely to fetch a decent price. Then you get the right PT for what you want to build. I think this is a better approach.

[johnnyreece]

I'd suggest is to use a full wave rectifier with choke input.

Just checking with an oddball idea; instead of a choke, couldn't one use a field coil speaker? I know it's out there, but some folks might have one on hand and wonder, "What can I do with this?" Just a thought!

[Stevem]

Good luck on trying to find a existing field coil speaker that can handle 50 watts of rms power!

[Phil_S]

I'd suggest is to use a full wave rectifier with choke input.

Just checking with an oddball idea; instead of a choke, couldn't one use a field coil speaker? I know it's out there, but some folks might have one on hand and wonder, "What can I do with this?" Just a thought!

What Steve says and, though it is a hefty choke requirement, it isn't *that* expensive. If this is going balls to the wall, choke input increases by about 1.5x for amps, so a 300mA Hammond choke will cost around $80. It will be less, depending on the requirements of the circuit. What you save on the PT, you spend on the choke. A new 174BX sells for around $150. There are choices to be made!

[johnnyreece]

Fair enough. Just trying to think outside the box a little. If power handling is an issue, it could be paired with another speaker(s). Again, this was on the off chance that OP had a field coil speaker laying around. I certainly don't advocate seeking one out!