Does anyone rewind power transformers or know someone who does? Any recommendation would be appreciated. I used to know someone in the 1980s but that was sooooooooooo long ago.
I have a vintage Futterman H3 in need of new iron and copper.
These transformers were too small for the job although this is the first one I've seen have problems.
I have a vintage Futterman H3 in need of new iron and copper.
These transformers were too small for the job although this is the first one I've seen have problems.
Thanks for the lead. Will take any others in case this doesn't work out. Have you had them build anything? This is about a 500 watt boat anchor.
It's hard to find one online that doesn't specialize in anything smaller than 100 KVA units. That's why I'm asking for recos.
Mercury Magnetics just rewound a Marantz 8B OPT for me. Not cheap, but a good job. Long lead time.
Nothing magical about Mr. Futterman's transformers.
Suggest it would be cheaper to replace them entirely.
Exact values for the B+ are not required.
The fils of course ought to be correct.
Also, back in his day the typical house voltage was ~10vac lower than it is now,
so this means that if you run an old school transformer, the voltages - especially the filaments - are higher than spec.
_-_-
Suggest it would be cheaper to replace them entirely.
Exact values for the B+ are not required.
The fils of course ought to be correct.
Also, back in his day the typical house voltage was ~10vac lower than it is now,
so this means that if you run an old school transformer, the voltages - especially the filaments - are higher than spec.
_-_-
Thanks bear.
I know there is nothing magic about JF's transformers other than their collector's value.
My line voltage here is around 120 consistently. You are right about older line voltages were looser in their tolerances. We just need it to work. Old varnish cooked off the windings. Am surprised I don't have a shorted turn. I have a HV sec to Faraday shield short. Probably could use it as is but there is a hi chance of a shorted turn happening soon.
JF went with a fairly hi temp rise to keep it small. He made OTL's because sweep tubes were cheap and plentiful and OPTs were expensive. The 40 to 60 watt range was in the ball park of most other amps. He wanted to make a cheap amp. The best speakers at the time were Quad 57's (might still be the best in many regards) and everyone used zip cord to their speakers. It was a simpler time. You really didn't know how good these were until everything else around these amps got better. Front end, wires, speakers etc.
Unfortunately the wire varnish of that era was not hi temp.
Actually voltages do matter in that circuit in terms of output power. And so does current. Will probably lower the volts a bit and adjust circuit for a bit more current to load if the winder can make that happen. The tubes can last longer.
Will be getting it rewound for 120 V input.
I know there is nothing magic about JF's transformers other than their collector's value.
My line voltage here is around 120 consistently. You are right about older line voltages were looser in their tolerances. We just need it to work. Old varnish cooked off the windings. Am surprised I don't have a shorted turn. I have a HV sec to Faraday shield short. Probably could use it as is but there is a hi chance of a shorted turn happening soon.
JF went with a fairly hi temp rise to keep it small. He made OTL's because sweep tubes were cheap and plentiful and OPTs were expensive. The 40 to 60 watt range was in the ball park of most other amps. He wanted to make a cheap amp. The best speakers at the time were Quad 57's (might still be the best in many regards) and everyone used zip cord to their speakers. It was a simpler time. You really didn't know how good these were until everything else around these amps got better. Front end, wires, speakers etc.
Unfortunately the wire varnish of that era was not hi temp.
Actually voltages do matter in that circuit in terms of output power. And so does current. Will probably lower the volts a bit and adjust circuit for a bit more current to load if the winder can make that happen. The tubes can last longer.
Will be getting it rewound for 120 V input.
Last edited:
Well as you wish.
The B+ is really not very critical. Like +/- 25vdc or more is nothing.
Have you seen pix of JF's "potting" area?
It was his kitchen stove, with a vacuum pump and a pressure cooker.
In his NYC apartment.
I'm not sure he wanted to make a "cheap amp" as much as he probably believed in the idea and wanted to make a living too.
The B+ is really not very critical. Like +/- 25vdc or more is nothing.
Have you seen pix of JF's "potting" area?
It was his kitchen stove, with a vacuum pump and a pressure cooker.
In his NYC apartment.
I'm not sure he wanted to make a "cheap amp" as much as he probably believed in the idea and wanted to make a living too.
OKBear.
Thanks for the reply.
The amp will run fine +/- 25 volts. That is less than 10% variation. But for better performance a regulated power supply is the bomb. It holds the B+ rock solid and helps eliminate feedback paths thru the decoupling caps to the front end. Imaging locks in like nothing else. I use Quad 63's I've modified. One of the most transparent speakers ever built but you have to mod them first.
I have built many revisions of the JFOTL. I built one with 24 output tubes. With only 16 we got 800 watts into 8 and 500 watts into 4 ohms. It did take 220 volts to make it talk but it worked. Never tested it with all 24. The mains in my shop were too small. But you could cook dinner on it.
Also, like any power amps, the maximum power out is directly related to the B+. Higher volts = higher headroom.
This was not Julius's only income. He was a test instrument engineer for, I think, Precision Test instruments on Long Island. But you could be right. Perhaps he really wanted to make a go of it. Transistors undid the dream in the long run. I think I recall Harvey saying he really wanted the amp to succeed and Harvey offered that possibility.
The amps have some design flaws but even with that they are amazing.
Never saw the pix of his potting area. Harvey had the pressure cooker with potting compound all hardened up, the top stuck to the bottom, and his fan for cooling them and we had a photo of it in his pamphlet. If you have that photo of his kitchen could you post or send it to me?
From what I garnered from being at NYAL (2 years as chief engineer) was that Julius was looking to make the amp cheaply and eliminating that stack of iron helped greatly. Again, in the 60's sweep tubes were cheap and plentiful. I was a TV repairman in the early 70's and replaced a lot of sweep tubes.
If transistors hadn't gotten traction it would have survived. But your Iphone would be a lot warmer.
Harvey was truly taken with what these amps could do and started NYAL to make them. I am still amazed by what they can do. Separation of instruments is superb and the top 2 octaves like no other amp. I am still a performing jazz bassist and these amps render cymbals better than anything I've ever heard.
Thanks for the reply.
The amp will run fine +/- 25 volts. That is less than 10% variation. But for better performance a regulated power supply is the bomb. It holds the B+ rock solid and helps eliminate feedback paths thru the decoupling caps to the front end. Imaging locks in like nothing else. I use Quad 63's I've modified. One of the most transparent speakers ever built but you have to mod them first.
I have built many revisions of the JFOTL. I built one with 24 output tubes. With only 16 we got 800 watts into 8 and 500 watts into 4 ohms. It did take 220 volts to make it talk but it worked. Never tested it with all 24. The mains in my shop were too small. But you could cook dinner on it.
Also, like any power amps, the maximum power out is directly related to the B+. Higher volts = higher headroom.
This was not Julius's only income. He was a test instrument engineer for, I think, Precision Test instruments on Long Island. But you could be right. Perhaps he really wanted to make a go of it. Transistors undid the dream in the long run. I think I recall Harvey saying he really wanted the amp to succeed and Harvey offered that possibility.
The amps have some design flaws but even with that they are amazing.
Never saw the pix of his potting area. Harvey had the pressure cooker with potting compound all hardened up, the top stuck to the bottom, and his fan for cooling them and we had a photo of it in his pamphlet. If you have that photo of his kitchen could you post or send it to me?
From what I garnered from being at NYAL (2 years as chief engineer) was that Julius was looking to make the amp cheaply and eliminating that stack of iron helped greatly. Again, in the 60's sweep tubes were cheap and plentiful. I was a TV repairman in the early 70's and replaced a lot of sweep tubes.
If transistors hadn't gotten traction it would have survived. But your Iphone would be a lot warmer.
Harvey was truly taken with what these amps could do and started NYAL to make them. I am still amazed by what they can do. Separation of instruments is superb and the top 2 octaves like no other amp. I am still a performing jazz bassist and these amps render cymbals better than anything I've ever heard.
Well...
If you were at that shindig at Harvey's warehouse with all the amps present, then we have met. I was the heretic with the DC coupled SE Mosfet amp. 😀
I am amazed you got so much power into 8 ohms - it has to be backed with current, of course.
There are better ways to do the OTL, imo. Kerim Onder had a nice circuit, but really required a DC servo and offset fault protection. Never got to build one. (puts another thing on personal bucket list)
I saw that pix online, many years ago on someone's site.
IF I saved it, it probably is on a somewhat defunct disc somewhere. 🙁
It likely still lurks somewhere. Did not know that Harvey had that pot!!
I visited NYAL when it was...where?... Croton?? some storefront, big Sound Labs speakers. He was selling a bunch of these multi chassis amps via Lyric Hi-Fi, iirc.
_-_-
If you were at that shindig at Harvey's warehouse with all the amps present, then we have met. I was the heretic with the DC coupled SE Mosfet amp. 😀
I am amazed you got so much power into 8 ohms - it has to be backed with current, of course.
There are better ways to do the OTL, imo. Kerim Onder had a nice circuit, but really required a DC servo and offset fault protection. Never got to build one. (puts another thing on personal bucket list)
I saw that pix online, many years ago on someone's site.
IF I saved it, it probably is on a somewhat defunct disc somewhere. 🙁
It likely still lurks somewhere. Did not know that Harvey had that pot!!
I visited NYAL when it was...where?... Croton?? some storefront, big Sound Labs speakers. He was selling a bunch of these multi chassis amps via Lyric Hi-Fi, iirc.
_-_-
P=EI = I2 R =E2/R take your pick. No current no power. 800 watt into 8 ohm is 10 amps.
From an engineering point of view, there are many ways to do the OTL. I did many variations and still kept Julius's circuit as the basis.
I have sitting in my house a pair of 200 watt/8ohm amps running triode. 10 output tubes each channel. I know how to make that happen.
The PL509's sold today are bogus. The do not pass the requisite 1.5 amps cathode current that real ones and 6LF6's do. They only do a 1/2 amp. If the real 509s were available I would have continued making them. But the market is tweaky and lots of incorrect lore abounds about the circuit and it is hard to market.
The 24 tube units had balanced split power supplied, and no output cap. Output stage was servo-ed.
The key to Julius's circuit is that it used a current starved front end with freq response that looked like a ski slope. It has an open loop gain at low frequencies of around 90 db but at high frequencies it was much lower, can't remember but it dropped off quickly, much like an op amp.
So the NFB at high freq. was much less in play. The input pentode has a 1.3 meg plate resistor. Current starved amps can only be made with pentodes which suppress the Miller effect.
I don't think Julius designed the amp with super performance in mind, just competitive performance so he could sell them.
That it turned out to be as good an amp as it was really wasn't on the radar until Harvey started promoting them. Supporting hifi gear wasn't that good in the 60's or 70's. Best speakers were e-stats.
I think you came to Croton before I started working there. So we may never have met. I don't know your real name so I can't say. Soundlabs were gone when I got there replaced with Quad 63's.
My quest for a xfmer winder has been answered, so thank you to everyone who made recommendations.
I went with TRS in Maine.
I must return to my music studies now.
From an engineering point of view, there are many ways to do the OTL. I did many variations and still kept Julius's circuit as the basis.
I have sitting in my house a pair of 200 watt/8ohm amps running triode. 10 output tubes each channel. I know how to make that happen.
The PL509's sold today are bogus. The do not pass the requisite 1.5 amps cathode current that real ones and 6LF6's do. They only do a 1/2 amp. If the real 509s were available I would have continued making them. But the market is tweaky and lots of incorrect lore abounds about the circuit and it is hard to market.
The 24 tube units had balanced split power supplied, and no output cap. Output stage was servo-ed.
The key to Julius's circuit is that it used a current starved front end with freq response that looked like a ski slope. It has an open loop gain at low frequencies of around 90 db but at high frequencies it was much lower, can't remember but it dropped off quickly, much like an op amp.
So the NFB at high freq. was much less in play. The input pentode has a 1.3 meg plate resistor. Current starved amps can only be made with pentodes which suppress the Miller effect.
I don't think Julius designed the amp with super performance in mind, just competitive performance so he could sell them.
That it turned out to be as good an amp as it was really wasn't on the radar until Harvey started promoting them. Supporting hifi gear wasn't that good in the 60's or 70's. Best speakers were e-stats.
I think you came to Croton before I started working there. So we may never have met. I don't know your real name so I can't say. Soundlabs were gone when I got there replaced with Quad 63's.
My quest for a xfmer winder has been answered, so thank you to everyone who made recommendations.
I went with TRS in Maine.
I must return to my music studies now.
Last edited:
Gary does good winding work. 😀
PM me or hit the email off my website, if you wish to continue chatting?
My recollections are that the Futterman amps were always regarded as exotic and desirable back in that 50-60s period.
PM me or hit the email off my website, if you wish to continue chatting?
My recollections are that the Futterman amps were always regarded as exotic and desirable back in that 50-60s period.
Another vote for TRS in Maine. Gary has done excellent work on the one power transformer I had him rewind. Wasn't cheap, but still cheaper than having a new one custom wound (oddball winding configuration from a British guitar amp). The only transformers he doesn't wind are bifilar wound. It takes too much time.
I will have to send these reco's to Gary to put the heat on to keep his high standards.
Glad to know I did something right. Even a stopped clock . . . .
Glad to know I did something right. Even a stopped clock . . . .
- Status
- Not open for further replies.