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Futterman H3

69.116.216.249
Posted on February 5, 2015 at 17:05:14
anthony.naso@hotmail.com
Audiophile

Posts: 34
Location: Northeast
Joined: March 13, 2009



hey all,

Attached is a set up sheet for the Futterman H3 OTL amp written up by JF himself from way back. I have used this for a while now (read years) to set up my Futterman OTL's. Never questioned the crossed out original numbers and the written in red new ones. Any thought on these changes from the rest of you guys? I suspect many of you have seen this before.

Thx A

 

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RE: Futterman H3, posted on February 5, 2015 at 17:16:46
anthony.naso@hotmail.com
Audiophile

Posts: 34
Location: Northeast
Joined: March 13, 2009



Maybe these will be easier to read

 

RE: Futterman H3, posted on February 5, 2015 at 17:18:43
anthony.naso@hotmail.com
Audiophile

Posts: 34
Location: Northeast
Joined: March 13, 2009



The other page

 

What's the question?, posted on February 6, 2015 at 08:05:14
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 I owned several pairs of "original" Futterman OTLs back in the day. I even had the privilege more than once of visiting Julius at his "factory" on W72nd St, off Broadway. Somewhere I have an instruction sheet for biasing my old H3aa's. As I recall, it does not have as many words of explanation as does yours. However, if Julius revised those numbers, I would go with it, if that's your question.

 

RE: What's the question?, posted on February 6, 2015 at 09:25:14
anthony.naso@hotmail.com
Audiophile

Posts: 34
Location: Northeast
Joined: March 13, 2009
 Thx for the reply. I have a copy of the H3aa bias plan as well and it is somewhat different. I do not know if these changes were made JF himself or not. I got this document years ago from someone and just started using it with no real issues but I was rebuilding my latest Futterman H3 amp and just for the 1st time said to myself... I wonder if...

1. Would it be better if the screen voltages were down at their original 225 volts as opposed to the revised 250 volts? Less heat???
2. Would it be better if the original 45 volts of negative bias remained as originally noted since the revised negative bias of 40 volts mean more current is being used?
3. Why change the bottom tube grid bias but not the top tube grid bias? Meaning why go down to -40v increasing the current draw on the bottom tubes but leave the original -180v from the cathode bias supply of the top tubes into their respective grids alone without change on the top tubes?

Those were my questions that came to mind on the latest rebuild,

Thx

A

 

RE: What's the question?, posted on February 6, 2015 at 10:02:27
anthony.naso@hotmail.com
Audiophile

Posts: 34
Location: Northeast
Joined: March 13, 2009
 Further to what I was feeling I just pulled my JF H3aa bias setup papers and it shows that 95v is to be at the front tube cathode as the requirement not 115 as was corrected on the papers I posted, and the NYAL OTL 1, 2 & 3 amps all use 85v at this same tube. I am beginning to think that maybe JF never made these corrections and that I have been blindly following this for years.

 

RE: What's the question?, posted on February 6, 2015 at 14:05:12
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 If you think you've been doing it "wrong" all these years, how did it sound? Apart from slight differences in tube life, I don't think 5% or 10% differences in voltages are going to do anything bad to the amp. Anyway, you can try some of the alternative values you've mentioned. If I can dig up my bias instructions from Julius, I will let you know what he recommended for my particular pair of H3aa's. Why would you think that's not his handwriting? Were those docs in anyone else's hands over the years? Ralph is pretty smart about Futtermans, too.

 

RE: What's the question?, posted on February 6, 2015 at 16:07:07
anthony.naso@hotmail.com
Audiophile

Posts: 34
Location: Northeast
Joined: March 13, 2009
 Thx again for responding.

No issues and my H3 amps have sounded fine. I will be trying the alternate voltages this weekend sometime. I got this doc from someone many years ago now via email and I cannot remember if I was told about the changes or who did them or if I even asked to be honest. Don't know why but the red pen says modern change not archival change from the days of JF.

Thx again

A

 

After all this time, posted on February 9, 2015 at 11:35:52
Ralph
Manufacturer

Posts: 4778
Location: Minnesota
Joined: April 24, 2002
 blindly following this for years.


If the amps have played OK and you've not particularly been bothered by short tube life, I would give it no further concern :)

 

RE: After all this time, posted on February 9, 2015 at 15:21:11
anthony.naso@hotmail.com
Audiophile

Posts: 34
Location: Northeast
Joined: March 13, 2009
 Thx Ralph, great answer. :)

 

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