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WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments

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Posted on August 7, 2020 at 07:34:42
rogerh113
Audiophile

Posts: 416
Location: San Francisco South Bay
Joined: October 20, 2014
I have now finished a couple of CD player fixes, and am still looking for a Futterman H3 to bring back to life. If you have an old one sitting around, please let me know.

I am looking at it as a chassis, transformer, some tubes, maybe some tube sockets, and the circuit schematic (which I will have to extract from the existing wiring and components). The electrolytics and resistors are well past their lifetime, so a complete rebuild will be needed to bring it up to some level of performance and reliability.

If you step up fast, you may be able to get a Classe CDP-1 or Audio Note AN-CD2 in trade (both are already listed for sale).

regards -- Roger

 

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Why not just get a Atma-sphere amp..., posted on August 7, 2020 at 16:54:57
Charlie8521
Audiophile

Posts: 879
Location: South East Michigan
Joined: October 2, 2004
new or used and be done with the screwing around? State of the art circuit design, high quality components, with factory product support. Just a thought for consideration.

 

RE: Why not just get a Atma-sphere amp..., posted on August 8, 2020 at 07:11:36
rogerh113
Audiophile

Posts: 416
Location: San Francisco South Bay
Joined: October 20, 2014
Sometimes the journey is as entertaining as arriving at the destination.

The Futterman is interesting by way of circuit design, and if it sounded very good with vintage components, I am curious to hear how it sounds with more modern (less vintage) components. For me, this would also be a learning experience as I go through the amp.

I am certainly not taking anything away from Atma-sphere. I have heard they are wonderful amps. You could say they are the same, as they are both OTL, but they are also very different.

 

Well then, why not jump in with..., posted on August 9, 2020 at 09:56:28
Charlie8521
Audiophile

Posts: 879
Location: South East Michigan
Joined: October 2, 2004
both feet. Build one from scratch. I would think you could get someone like Heyboer Transformer to build the Power Transformer, get a schematic with all of the recommended changes, and then utilize high grade components and wiring. Everything brand new, and it would be an experience with something in the end to talk about for years.

 

RE: Well then, why not jump in with..., posted on August 10, 2020 at 07:52:20
rogerh113
Audiophile

Posts: 416
Location: San Francisco South Bay
Joined: October 20, 2014
I have actually considered that, but there are a couple of reasons I opted not to go that way.

I have built a large tube amp from scratch, and enjoyed it a lot. There is a LOT of work in properly setting up the chassis. I simply am not so interested in doing that again. I do enjoy component sourcing, wiring, and learning about circuit operation, and would prefer to concentrate on that. At close on to 67, best to spend your time how you like to....

The various Futterman implementations seem to have variation from amp to amp, and not just the tube complement. Taking a working (or at least formerly working) example at least gives me a functional starting point.

 

OK, maybe post an Ad..., posted on August 10, 2020 at 11:31:35
Charlie8521
Audiophile

Posts: 879
Location: South East Michigan
Joined: October 2, 2004
on the AudioAsylum Trader section, Wanted Futterman. Or do the same on Audiogon site. Good luck in your quest.

 

RE: Why not just get a Atma-sphere amp..., posted on August 10, 2020 at 12:35:28
airheadair
Audiophile

Posts: 389
Location: California
Joined: October 18, 2010
I can say that the NYAL OTL3 sounds fantastic with Stax F83 speakers. But these are probably "vintage" components now. Interestingly, they run rather cool, compared to what I have heard about the Atmosphere amps. As you say, the circuit is very different. Some people prefer one, some the other. It probably depends also on the application.

 

Jon Broskie says they are the same, posted on August 14, 2020 at 11:54:37
Lew
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Posts: 10767
Location: Bethesda, Maryland
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If you read Tubecad, Broskie, who doesn't shy away from making provocative generalizations, says the circlotron and the Futterman output stages are fundamentally the same. I personally cannot see how that could be true, but I'd love to see Ralph's take on the idea. My last pair of Futterman amplifiers were Prodigy amplifiers, out of Texas. They sounded excellent driving the Sound Lab M1s I owned at that time (early 90s). Arguably, the Sound Labs are "modern". However, they presented a booby trap for either type of OTL, there was a very low impedance dip at midrange frequencies, as low as 2 ohms at between 1kHz and 2kHz. Neither Futterman nor circlotron is happy with that load at those frequencies.

 

RE: Jon Broskie says they are the same, posted on August 14, 2020 at 13:50:03
airheadair
Audiophile

Posts: 389
Location: California
Joined: October 18, 2010
The Stax F83's have a strange impedance curve: about 4 ohms at both frequency extremes, about 160 ohms in the middle. I now use a subwoofer for the bass (crossing over at 100 HZ), so that part of the story is out of the picture. I guess the remaining high impedance makes up for the very low efficiency, making the NYAL OTL a good match.

 

Heard it before., posted on August 18, 2020 at 10:11:07
Ralph
Manufacturer

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Location: Minnesota
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But its not the case. You get a little bit lower output impedance with a Circlotron, and you certainly get to use a lot more intuitive circuit to drive it :)

But you're right, he likes to be provocative.

 

RE: Jon Broskie says they are the same, posted on September 21, 2020 at 07:58:48
cpotl
Audiophile

Posts: 1002
Location: Texas
Joined: December 6, 2009
"If you read Tubecad, Broskie, who doesn't shy away from making provocative generalizations, says the circlotron and the Futterman output stages are fundamentally the same."

That's not quite what he says. His whole point in that article is that what really matters, when you analyse the circuits, is where the signal reference point is in the output stage. As he says, the signal ground reference point is different in the circlotron and in the totem pole, and so they behave differently. However, he also points out that with a small change in how the ground reference point is set (by taking the signal ground to be at the midpoint between the two speaker terminals rather than at one end), then the totem pole would become operationally equivalent to the circlotron. I think that is an uncontroversial point.

 

Thanks for the correction,,,,, posted on October 10, 2020 at 13:58:03
Lew
Audiophile

Posts: 10767
Location: Bethesda, Maryland
Joined: December 11, 2000
Perhaps I faded out before completely comprehending Broskie's thought on this subject. As an OTL devotee, I want to understand it, so I will search it out and re-read it.

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on June 23, 2022 at 10:18:40
unlisted
Audiophile

Posts: 24
Joined: March 21, 2014
Still interested?

I have a NYAL OTL-3 pair, but one amp just lost a power supply cap when doing the electrical setups (the other is fine). A shame as I just installed a complete unused dozen set of RAM Lab 6LF6's for them and the other tubes are all very strong.

I can't complain. George Kaye said the first ones, like mine, used WWII surplus power supply caps in some of them when he redid the amps for me.

It's been awhile since I've been on this site, but I know this is a bigger job than I want to tackle. If interested please let me know. (I'm in NM)

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on June 24, 2022 at 04:39:18
rogerh113
Audiophile

Posts: 416
Location: San Francisco South Bay
Joined: October 20, 2014
Thanks for the reply. I found an H-3 several months ago, and am mid way through the rebuilding process. Having a lot of fun with it !!

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on June 25, 2022 at 07:30:29
unlisted
Audiophile

Posts: 24
Joined: March 21, 2014
Thank you for the quick reply. And I'm glad you found an OTL.

I'm not certain what to do with mine. I've seen "rhinohifi714" post some of his work and I'm envious.

All the best!

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on June 25, 2022 at 07:51:22
rogerh113
Audiophile

Posts: 416
Location: San Francisco South Bay
Joined: October 20, 2014
It is likely that if one of the power caps failed, then the other similar caps (in both units) also are at end of life. Could also be some other tired components - slow degradation of sound can be missed since you constantly adapt to the 'new sound'.

Perhaps you can post a picture of the inside of one of the amps. Could be that these use circuit boards (rather than point to point), which have their advantages and disadvantages.

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on June 25, 2022 at 08:14:59
unlisted
Audiophile

Posts: 24
Joined: March 21, 2014
Yes, one of the power caps did fail. Given the age of the amps I think replacing the power supplies in both would be the prudent course of action to keep them healthy.

If I could find two new OTL3 boards I might redo them entirely.

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on June 25, 2022 at 08:19:41
rogerh113
Audiophile

Posts: 416
Location: San Francisco South Bay
Joined: October 20, 2014
Why do you need new boards? Generally PC boards can be reworked without too much trouble, unless the boards are poorly made and the traces lift. Also an opportunity to put in new rectifier diodes, and take care of the other aged electrolytic caps.

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on June 25, 2022 at 08:59:54
unlisted
Audiophile

Posts: 24
Joined: March 21, 2014



Yes, you're right. There's nothing wrong with the circuit boards per se. The concern is that these are very early OTL3 models and the schematics I have do not match this amp. I posted a picture years ago and "rhinohifi714" noted seeing several differences. The biggest concern is some of the transistors I see under the board have no markings and it is not possible to identify possible replacement(s).

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on June 25, 2022 at 09:43:20
rogerh113
Audiophile

Posts: 416
Location: San Francisco South Bay
Joined: October 20, 2014
The boards look good - interesting all of the soldered in fuses...

You would really need to know what the rest of the amp is set up for before putting in uplevel boards. Could be that the elements that interface with the boards might be different / have different values (like voltage). Not familiar with these amps, so don't know what resides off of these boards.

Generally the transistor cans are marked. If they are easy to access, you might try good lighting and a magnifying glass. Sometimes changing the angle of the incident light helps to reveal the markings, particularly if they are old and weakly printed.

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on June 25, 2022 at 10:30:53
unlisted
Audiophile

Posts: 24
Joined: March 21, 2014
That's a good point about checking for an uplevel board setup. George Kaye kindly gave me the setup information when he last worked on the amps and they look like standard OTL3 set points, but it's always good to double check. Fortunately, the other amp is working fine so I have a baseline.

I spent quite a lot of time trying to identify the transistors, but other than ubiquitous TO-92 cases I was unable to find any markings even with magnifying glasses and excellent lighting on either amp.

I had George Kaye update the audio circuits with new resistors and caps, given the substantial improvements in component transparency and electrical behavior over the years, along with any other updates required (Dynamicaps, Black Gates, Vishay, Audio Note, etc.). For this reason I think the board and components are in good shape, but I do worry nonetheless. New capacitor power supply banks would certainly get them working optimally now.

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on June 25, 2022 at 12:14:32
rogerh113
Audiophile

Posts: 416
Location: San Francisco South Bay
Joined: October 20, 2014
Given the prior upgrades, sounds like the best approach is to just upgrade the suspect power caps. Get the caps for both sides and do the broken side, keeping the working side as a reference. When the broken side works, then you can go after the other side.

With all of those fuses, the amp is likely pretty well protected....

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on July 1, 2022 at 13:00:30
rhinohifi714
Audiophile

Posts: 164
Location: oklahoma
Joined: June 13, 2009
looks good

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on July 1, 2022 at 13:45:55
unlisted
Audiophile

Posts: 24
Joined: March 21, 2014
Thanks. I've seen of some of your refurbishments on this site and they're very impressive.

I'm undecided on if I'm going to replace all the electrolytic power caps. If I do, any pointers or suggestions?

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on July 1, 2022 at 17:07:54
rhinohifi714
Audiophile

Posts: 164
Location: oklahoma
Joined: June 13, 2009
since you have had one of the original capacitors fail it would be a good idea to put all new ones in, as well as the ones on the board.

https://www.ebay.com/itm/123867313130

use 6 of these per amp, 4 for power supply and 2 for the speaker bank, the amount of capacitance will be very close to the original configuration.
these are photo capacitors with the same voltage as the Rubicon's that were stock.

I have used new computer grade capacitors in a few of the rebuilds I did,
but personally I think the new Photo Flash are the way to go.

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on July 1, 2022 at 17:28:32
rhinohifi714
Audiophile

Posts: 164
Location: oklahoma
Joined: June 13, 2009



when you put the new tubes in did you re-align the amp?
If not then that is probably the reason the capacitor failed.

 

RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on July 1, 2022 at 17:29:59
rhinohifi714
Audiophile

Posts: 164
Location: oklahoma
Joined: June 13, 2009



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RE: WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments, posted on July 2, 2022 at 07:41:23
rhinohifi714
Audiophile

Posts: 164
Location: oklahoma
Joined: June 13, 2009
https://www.ebay.com/itm/265657260460

 

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