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Model H-3 OTL

205.188.116.16
Posted on April 21, 2009 at 18:51:37
loucev
Audiophile

Posts: 2
Location: New Jersey
Joined: April 21, 2009
 Please under stand first off that I have a limited education in tube amps,let alone this Futterman that I found in a family members basement. I powered it up gently with a Variac, all the tubes lit nicely. I left it powered up for 20 or so minutes...no smoke. I then connected a Apt Holman pre amp I had laying around, with a CD player and a pair of speakers. One side is out. I checked the bottom and didn't see anything burned or charred, or anything that had a hint of smell.
I then started to look at the tubes. The larger group of 4 output tubes (?) are marked on the base as 6HJ5's. Instead there are 6KG6A's in their place. I looked thru the book of my tube tester, and it dosent list the 6KG6A/EL509, so I cannot test them. In the center, it reads 6DR7,and its actually a 6FD7. Also, where there is suppose to be a 6EM7, there is a 6LR8.
One more oddity is that where there is a spot for a Grid Bias V1-V2(a and B) pot, there lies just a hole. There dosen't appear to be any cut wires on the bottom of this unit.
Before I get crazy with this amp, I would like some of your input as to what this amp might sound like with a Mac C27 pre and a set of mid 70's Klipschorns.

HELP !!!

RE: Model H-3 OTL, posted on October 4, 2009 at 23:01:33
lucisfero1
Audiophile

Posts: 3
Location: NYC
Joined: August 17, 2000



As the pix shows, 6KG6A is the same as the EL509.

I can also send pix of the other tubes used in the Futterman

Julius had his shop on w72 street in NYC (building is now torn down) and he would came over my house to modify the H3a which I used to power my KLH-9's at the time. That amp STILL FUNCTIONS.

I think a lot of people speak about these amps without actually listened to one or actually owning one.

RE: Model H-3 OTL, posted on August 23, 2009 at 15:16:51
loucev
Audiophile

Posts: 2
Location: New Jersey
Joined: April 21, 2009
 Well, I've done nothing to the Futterman H3 that I found in Grandpa's basement.One side is still out. I went back to see what else I could find, and came up with a set of Futterman H3aa Monoblocks using 6- 6LF6's. After slowly firing them up with my Variac, I hooked them up to a pre amp and a CD player and........one side sounds awful and the other side clean but started a loud popping sound, so off it went. So now I have 2 Futtermans that need work and I am not qualified to do it. Any thoughts as to who might be a good choice to trust to fix these gems? Keep in mind that I am not a wealthy man.
Lou Cevetello

RE: Model H-3 OTL, posted on August 23, 2009 at 18:56:47
QuinnLing
 You can try George Kaye
RE: Model H-3 OTL, posted on April 26, 2009 at 10:42:58
AJ
Audiophile

Posts: 268
Joined: February 24, 2001
 Hi I have a H-3 by Harvard Electronics. Tech Instruments also produced the H-3.

It is quite possible that the small tubes you mention (pass regulators) are part of the original circuit regardless of what is printed on the chassis .This is what happened to me in the noted link.

If you have the original set up voltage procedure I would check voltages at the plates and screens + bias as instructed to see if you are ok.

My H-3 runs 6FW5's which is equivalent to the 6HJ5 in octal rather than compactron form. It also may be that someone has converted to 6KG6?

AJ

RE: Model H-3 OTL, posted on April 23, 2009 at 15:36:30
Ralph
Manufacturer

Posts: 1156
Location: Minnesota
Joined: April 24, 2002
Contributor
  Since: April 1, 2002
 FWIW. the EL509 is really just about the only game in town for the power tube in amps like this, so if it is working with these tubes it would seem that you have no worries- the tube is still made.

RE: Model H-3 OTL, posted on April 22, 2009 at 12:47:09
Lew
Audiophile

Posts: 2685
Location: Bethesda, Maryland
Joined: December 11, 2000
 Below is a URL that will take you to a discussion of your amplifier that was on this website 3 years ago; I happened to come across it. The words of wisdom will be helpful to you.

http://www.audioasylum.com/scripts/t.pl?f=otl&m=30763
Wow!, posted on April 22, 2009 at 12:43:57
Lew
Audiophile

Posts: 2685
Location: Bethesda, Maryland
Joined: December 11, 2000
 This is the second Futterman H3 amp that has turned up on this thread in the past 2 months, whereas, I had not seen or heard of one of these for a few decades before now. Does it say "Harvard Electronics" somewhere on the chassis? I presume it's a stereo amp (two channels on one chassis). If yes to both questions, your amp is very old. Goes back to 60's at the latest.

I cannot answer all of your questions about the tube alternatives. The 6EM7 and 6LR8 are dual section tubes where one half is a triode and the other half is a pentode (pretty cool). The 6LR8 is not listed as a drop-in replacement for the 6EM7, however. You might want to do some internet searching to find data for the 6HJ5 vs the 6KG6A (these are the pentode power tubes on the amp). You imply that 6KG6A is equivalent to a PL509; I was not aware of that, but you could be correct. Likewise, look in a tube database to find whether 6DR7 and 6FD7 are interchangeable. Other than getting the tubes under control, you should almost certainly replace all the electrolytic caps, especially the output coupling caps. Once refurbished, this is a fine sounding amp and should sound good with any speaker that has an average impedance above 4 ohms, preferably above 8 ohms.

RE: Wow!, posted on April 22, 2009 at 14:58:33
glenz10183
 Julius Futterman manufactured some of his OTL amplifiers under the Harvard name.


Best,

George

RE: Wow!, posted on April 23, 2009 at 07:15:29
Lew
Audiophile

Posts: 2685
Location: Bethesda, Maryland
Joined: December 11, 2000
 I guess I failed to say that, but that was why I asked the question. The poster told me in a private e-mail that the unit says "Tech Instruments" in Woodside, NY. If memory serves, that was also a Futterman business, or perhaps the same business under another name (other than "Harvard").

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