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Futterman H3 Blowing Fuse

69.181.30.196
Posted on September 25, 2006 at 22:15:06
vacumtubes
Audiophile

Posts: 10
Location: San Francisco
Joined: May 26, 2004
 I am restoring a Futterman H3 stereo amp (Harvard Elec). This one uses 6EJ7, 6FS5, 6DR7, 6EM7 if that helps. It is blowing fuse after a minute or two. I believe the output tubes (6HJ5) are weak and can not source 8 good ones. If I fire it up without the 6HJ5, it does not blow the fuse. Not sure if I should source 6HJ5 or convert to a different tube.
Is there an easy tube conversion to replace the 6HJ5? Was thinging of EL509. May not be as easy to convert as 6LF6, but avilable.
Any help is appreciated. The guys at moscode may charge a pretty penny to get it all running with conversion. I would be willing to pay reasonable repair/conversion cost, but who knows when they say "Send it in first".
I plan to use it with stacked Quad 57.

Re: Futterman H3 Blowing Fuse, posted on November 2, 2009 at 06:59:51
Jimmyblues
 I owned a Futterman H-3 about two decades ago and found it to be a great sounding piece of gear with plenty of power to drive the 15 OHM Rogers LS 3/5A's I was running at the time.

I sold it to a fellow in Japan back in the early 1990's when the vintage hi-fi craze was in full swing. I miss the amp but have always been concerned about the transformers on such old amplifiers burning out. I have a few classic solid state preamp's from the mid 80's and several vintage broadcast tuners (including a few McIntosh MR-65B's) going back as far as the early 1960's. However, their transformers are not under the same stress as those of a vintage amplifier.

As for tube amplification, I eventually chose to purchase some new tube monoblocks from Quicksilver and Antique Sound Lab - they don't have the same cache as an old Futterman, Leak or Quad, however they are much newer and with "warm up" circuitry that does not stress them out.

Enjoy the music!

Jimmyblues

Re: Futterman H3 Blowing Fuse, posted on September 26, 2006 at 21:46:02
AJ
Audiophile

Posts: 268
Joined: February 24, 2001
 Hi, I've got one of these running on the ESL 57. Mine uses the 6fw5 octal which is cheap and plentiful...last I looked the 6fw5 and the 6hj5 are exactly compatable, one being a compactron the other octal..you can make the switch but I'm sure you can find the 6hj5's. Futterman used whatever worked or he had on hand. You can check the specs on TDSL. You can pick up 6FW5's all day long for $3-4..As for the 6hj5's they should almost give them away too...maybe you're not looking hard enough?

Careful on this amp the ac primary is not fused you could burn a transformer up quick if you don't know what you're doing

For example, my unit is labled with 7734 on the chassis for the upper screen regulator while infact ,it actually uses the 6DR7..they never changed the silkscreening on the chassis! A year or two after I got the amp I noticed the faint outline of what would have been a sticker covering up the 7734 label ... the sticker probably burnt up years before. I figured the 6DR7 thing out after the 7734 would glow cherry.

Before you make any judgements on this amp you MUST change all those lousy goodall caps with good quality film types.Also change the output electrolytics and powersupply caps... they are available from Allied or Mouser in the same form factor. I'm going to experiment with film caps on the output but it involves a bit of a modification to fit the larger diameter film cap and I just never got around to it.

Anyway, they do sound great on the ESL..finicky as hell to initially set up but once you get used to it .... it is a great amp...check out vintage asylum under "Joe Rosen" and Futterman for interesting reading.

Don't know what tubevib is saying I think he means impedance matching autoformers for your speakers ...you don't need this & has nothing to do with your problem. If you're running the Quads stacked just hook them up in series, just like Futterman himself recommended and enjoy.

I have Futterman's original bias and set up procedure on this amp in pdf. E-mail me through the board if you'd like a copy.

AJ
Re: Futterman H3 Blowing Fuse, posted on September 27, 2006 at 22:44:48
vacumtubes
Audiophile

Posts: 10
Location: San Francisco
Joined: May 26, 2004
 Thanks for your posts.
I do have the original bias procedure for the H-3 already.

Hopefully the 6HJ5 is all that is wrong with the amp. The diodes are good, and the caps are not open or shorted, did not test capacity. I need to call a store that listed 6HJ5 (various brands) to find out it they are what they claim. At least they are only asking $6.00 each. The 6FW5 is really close, and should work with a socket change.

And thanks AJ, I do know the primary is not fused, and transformers are known to blow on these. I've been bring it up on a variac and checking voltages as I go along.
Ive been blowing the 1.5A fuse after the bridge.

The coupling capacitors in mine are Mallory so they may have been changed. I should replace them anyway, along with the electrolytics.

I will try my stacked 57 in series, and with the Zero's that I have.

Thanks again and any more feedback is appreciated.

vacumtubes

Re: Futterman H3 Blowing Fuse, posted on September 26, 2006 at 10:25:28
Bob A
 If you go 509 be sure to source a replacement set. I don't think that tube is in production anymore. I know the 519 is getting scarce. (No longer in production.)

Re: Futterman H3 Blowing Fuse, posted on September 26, 2006 at 07:43:51
DaveInVA
Audiophile

Posts: 1464
Location: Danville VA
Joined: June 21, 2001
 I worked on one of those a long time ago but I can't remember if it was an H3. It did the same thing and it used photoflash capacitors to block the dc to the speakers and they were bad. Hope this helps some.

Dave

Re: Futterman H3 Blowing Fuse, posted on September 26, 2006 at 04:44:01
tubevibb
 You got to get AUTO-FORMER,S that all i no!

Re: Futterman H3 Blowing Fuse, posted on September 26, 2006 at 08:17:45
Legendre
Manufacturer

Posts: 455
Location: Saint Paul
Joined: October 22, 2004
 What are you on about now, tubevib? An autoformer has nothing to do with this issue...

And what's preventing you form registering a nickname / moniker? :-)

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