Harman Kardon A700 amp or TA7000 receiver power transformer number?

[GordonW]

Hi- need some info.

Anyone who has an HK A700 integrated amp, or TA7000 receiver- could you take a look at the power transformer, and post up the number that's on top? It should start with "FT" as the first two characters.

I have a power transformer here, that I am 90% sure is from one of these (it has exactly the right sort of connections, for B+, bias and heaters, it's the right size and shape, and it has a "FT" number), but I would like to know for sure, so I can arrange to use appropriate loads on it (for heaters and such).

Thanks!

Regards,
Gordon.

 

[Tinkerbelle]

From an old (completed) listing it looks like FT7297901, or *681 or *081, or *891 - tough to read those last numbers

 

[mpholland]

From an old (completed) listing it looks like FT7297901, or *681 or *081, or *891 - tough to read those last numbers

I'm thinking you saved the best for last.

 

[GordonW]

Well shoot- mine starts with FT2382. Definitely not that one.

Regards,
Gordon.

 

[Tinkerbelle]

I'm thinking you saved the best for last.

Oh, my eyes aren't as bad as I thought then

Gordon, I think the TA-7000 PT is a different PN from the A-700 due to added circuitry for tuner section but the schematic seems to indicate FT4727368 for that receiver. Also, the A260 Chorale has FT2963803 & the HK250 (6L6) is FT2382665, so perhaps is an HK250, good for 6L6s

 

[kward]

Did someone say 6L6's? I hear Gordon has a soft spot for those... Maybe we'll see "Ship in a bottle" amp #4 soon.

 

[GordonW]

... the HK250 (6L6) is FT2382665, so perhaps is an HK250, good for 6L6s

DINGDINGDING! BINGO! WINNER!

That's it.

And that's really cool, as I'm planning to build a 6L6 amp out of it. Got a pair of Sherwood output transformers that are 5500 ohms into 4/8/16 ohms, that will go great with it. The only difference, is that I'm planning to run fixed bias (unlike the cathode bias of the HK250)- with the Sherwood transformers, the sims I've run say I should be easily able to get 30w/ch, maybe more...

The only odd thing (and why I thought it may have been used with 7591s) is that this one has a 15v secondary winding, in addition to the plate and heater windings. Great for me (I can voltage-double it, instant bias supply), but it doesn't fit in with any of the HK250 schematics I have seen...

Regards,
Gordon.

 

[Tinkerbelle]

That sounds like a good combination with the Sherwood OPTs.

There is an A-250, which has a 17V secondary winding...

 

[Tinkerbelle]

The A250 also uses 6L6s and the PT is FT2382665, with 6.3V, 150V and 17V secondaries.

 

[GordonW]

Mine must be the A250 version!

It's FT2382665B on my transformer. 'B' probably refers to a production change, adding the 17v winding.

In any case- 17v voltage-doubled makes a perfect bias supply for fixed bias...

Regards,
Gordon.

 

[TriodeLuvr]

And that's really cool, as I'm planning to build a 6L6 amp out of it.

Gordon, did you ever pursue this project? I'm just now finishing an amplifier using all the iron from a TA7000X. The new amp is 6L6-based, rather than 7591.

Jack

 

[GordonW]

Gordon, did you ever pursue this project? I'm just now finishing an amplifier using all the iron from a TA7000X. The new amp is 6L6-based, rather than 7591.

Jack

The Sherwood output transformers came from BuzzK- and he, while replacing the lead-out wires on the transformers with new wires- found a pair of UL taps!

I wound up using these transformers to build an EL34 UL amp, using the Eico HF60 circuit, as modded by Dave Gillespie for triode front end. Integrated amp, with 6SN7 preamp, amp voltage stage and LTP inverters. This was my "True Blue" amp

https://www.audiokarma.org/forums/i...-is-now-doing-its-thing.831340/#post-11832098

Regards,
Gordon.

 

[TriodeLuvr]

That's a nice amp! Unfortunately, it doesn't seem in any way related to what I've built. After reading through this thread again, I see the PT isn't from the TA7000X, but rather the A250. So, yours is very different - EL34s, UL, +360V B+.

My interest in all this has to do with the output power of the A700 and TA7000X. I couldn't measure the TA7000X before it was disassembled, and my version with 6L6 output is well short of the original 35W/ch rating, even with only one channel driven. The limitation appears to be simply insufficient B+. With one channel at full output, B+ is about +425V. That produces about 30W, and it's closer to 25W with both channels driven.

Anyway, I don't want to hijack this thread. I was going to raise this topic in a separate post, but what I really need is a comparative measurement. The A700 and TA7000X aren't very common, so that's probably not likely to happen. Thanks for getting back to me!

Jack