Could someone tell me if the output transformer found in a Eico st-40 would be a suitable replacement for the Heathkit W5. I am currently rebuilding a Heathkit W5 that came with a Hammond 1620 output transformer. The reason I ask is that I’m considering a 2nd w5 and wondering what I should do. Should I use a pair of Eico ST-40 output transformers or just purchase an additional Hammond 1620.
Heathkit W5 Output transformer
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I never thought about that but I think the Eico ST40 output transformers will work as replacement for the W5 output transformers, with some tweaking of feedback of course. My recollection is that the ST40 transformers have 8250 Ohm primaries (google thought so too) and will work better in the W5 Williamson circuit than the Hammond 1620 with 6600 Ohm primaries. The original W5 16309 outputs showed 8600 Ohm primaries. If you have a pair of Eico ST40 transformers on hand I’d say go for it.
Dave Gillespie’s thread on the “Untapped potential:Heathkit W5m” has lots of info on the output transformers in post #5.
Dave Gillespie’s thread on the “Untapped potential:Heathkit W5m” has lots of info on the output transformers in post #5.
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I'm confident you will get better overall performance out of the Eico ST-40 output transformers than the Hammond 1620. In stock form, the Heathkit adds I think about 20 dB of global negative feedback. How much feedback you can add depends on the quality of the output transformers. Can you get to the stock 20 dB GNFB level with the Eico ST-40's in the Heathkit W5M circuit? Not sure, but I think you will have a much better go at it over any 16xx-line Hammond output transformer. Also be aware the 1620 uses what I will call their "traditional" secondary winding method. That means the secondary is not one continuous winding with taps at 8 and 4 ohms. With the traditional Hammond secondary winding method, you get either 16 ohms, OR 8 and 4 ohms, but not all three simultaneously.
What I can say about the traditional Hammond secondary winding approach is they produce stellar LF response, but you need to make some fairly serious compromises on amplifier transient tuning to squeak out reasonable performance in the HF. Typically you would not want to add more than say 10 to 12 dB of GNFB with their traditional winding secondaries so that you stay away from the HF shortcomings of these transformers.
On the other hand if you are talking about the new "A" winding method of the Hammond secondaries (e.g., the 1620A in this case), then it does use one continuous 16 ohm wind with taps at 4 and 8 ohms. I have zero experience with the "A" secondary winding method from Hammond...maybe others do, and these might be okay.
Of course, you could purchase an old stock set of 16309's. They do come up for sale from time to time on the auction site. It might take you 6 to 12 months to source a pair though. The W5M is a very capable amplifier when properly restored/tuned, so I would say use the best iron you can find, and I think there are better choices than Hammond for the Heathkit W5M.
What I can say about the traditional Hammond secondary winding approach is they produce stellar LF response, but you need to make some fairly serious compromises on amplifier transient tuning to squeak out reasonable performance in the HF. Typically you would not want to add more than say 10 to 12 dB of GNFB with their traditional winding secondaries so that you stay away from the HF shortcomings of these transformers.
On the other hand if you are talking about the new "A" winding method of the Hammond secondaries (e.g., the 1620A in this case), then it does use one continuous 16 ohm wind with taps at 4 and 8 ohms. I have zero experience with the "A" secondary winding method from Hammond...maybe others do, and these might be okay.
Of course, you could purchase an old stock set of 16309's. They do come up for sale from time to time on the auction site. It might take you 6 to 12 months to source a pair though. The W5M is a very capable amplifier when properly restored/tuned, so I would say use the best iron you can find, and I think there are better choices than Hammond for the Heathkit W5M.
The output transformers are the main thing you are buying when buying a vintage amplifier, and yes a W5M without the Peerless OPT is not worth very much. If I was looking I would maybe go with the 16458 though.
Fisher or Scott transformers would work as well. I’d want both amps to be the same.
Dave G said the UL taps were done wrong and hurt performance. So he went pentode fixed bias EFB and all that jazz. The Scott and Fisher stuff had no UL taps.
I watch W5’s on EBay. Just for fun. Amazes me that sellers want big money for untested amps. Those could quite easily be an expensive boat anchor.
I acquired 4 of these in the early 90’s. 2 with 16458’s and someone’s hack job of replacing power transformers. 2 with 16309’s and orig pwr transformers. Total investment was less than $100.
I still have and use them. The 16458 units have 6B4g outputs and the 16309 are running EL34 in triode mode.
Dave G said the UL taps were done wrong and hurt performance. So he went pentode fixed bias EFB and all that jazz. The Scott and Fisher stuff had no UL taps.
I watch W5’s on EBay. Just for fun. Amazes me that sellers want big money for untested amps. Those could quite easily be an expensive boat anchor.
I acquired 4 of these in the early 90’s. 2 with 16458’s and someone’s hack job of replacing power transformers. 2 with 16309’s and orig pwr transformers. Total investment was less than $100.
I still have and use them. The 16458 units have 6B4g outputs and the 16309 are running EL34 in triode mode.
By the way I don’t mean to disparage Hammond transformers as much as it may have sounded. I’ve built some great sounding amps with the 1650H and 1650R output transformers. It’s just they all exhibit similar HF issues that need to be dealt with. There is no perfect OPT but the peerless line used in the W5 come as close as some of the best I’ve seen like Fisher 400 and 500C and such.
There's a pair of 16309s on the bay now. There's also a listing for a 16458, but that is not what it is. If you're considering a second W5, it would be worth the effort to find a Peerless output to match, otherwise they won't sound the same at all.