Recent Posts

61

Tube Amp Building - Tweaks - Repairs / Re: 6M5 6EM5 Valves in Push Pull

« Last post by kagliostro on October 20, 2025, 03:54:46 am »

... V3 probably needs to do a 20mm Offset towards centre of chassis?? and a real pain to do ...

Aluminium sheet on the top of the chassis (small if you don't care, large as the chassis top if you prefer) and new holes ?

(may be a little shield between Tube and Transformer too ?)

Franco

62

Tube Amp Building - Tweaks - Repairs / Re: 6M5 6EM5 Valves in Push Pull

« Last post by glass54 on October 20, 2025, 01:35:59 am »

Hi Timbo,
V3 probably needs to do a 20mm Offset towards centre of chassis?? and a real pain to do 
Silly question (and way toooo late) How come you didn't do the 4 sockets "in  line" along chassis.
You may have got away with it.
Regards
Mirek

63

Tube Amp Building - Tweaks - Repairs / Re: 6M5 6EM5 Valves in Push Pull

« Last post by TIMBO on October 20, 2025, 01:14:00 am »

Hey guys, Just when you think you are on the home stretch

 

Lucky they make holes in speaker baskets nowadays…

The problem is the valve hits the basket

64

Tube Amp Building - Tweaks - Repairs / Re: Hoffman Single Channel AB763-1 Annoying 60Hz Buzz

« Last post by AlNewman on October 20, 2025, 12:26:01 am »

Can you isolate the problem?  I happens with the reverb level at 0?  What happens if you unplug the reverb tank?  Ground the grid of V3a pin 2?   Ground the grid of V3b pin 7?

65

Tube Amp Building - Tweaks - Repairs / Re: Hoffman Single Channel AB763-1 Annoying 60Hz Buzz

« Last post by tubeswell on October 19, 2025, 07:11:28 pm »

Latest.I moved some grounds.  The issue now is that the entire amp chassis is microphonic.Pull V1 preamp.  No change.Pull V2 reverb driver.  No change.Pull V3, reverb recovery / PI driver.  Totally silent.I tried three different tubes in V3, a new JJ, and NOS GE, and a NOS RCA.  The entire amp is microphonic no matter which one.I'm going over the V3 circuit with a fine-tooth comb, but so far, nothing.

There is a component in the signal path with a loose connection.

Check that all input jack tip-switch contacts are making firm connection with the jack tips when there is no plug inserted. Even a slightly open connection will rattle microphonically. You can verify this by pressing the tip switches against the tips to see if the hum stops. The fix is to re-tension the tip switches slightly to make firm contact.

66

Tube Amp Building - Tweaks - Repairs / Re: 6M5 6EM5 Valves in Push Pull

« Last post by tubeswell on October 19, 2025, 05:33:16 pm »

Hey guys, Just when you think you are on the home stretch

 

Lucky they make holes in speaker baskets nowadays…

67

Introduce Yourself / Thanks for your service!

« Last post by EL34 on October 19, 2025, 03:11:01 pm »

Welcome to the Hoffman Amps forum

There are many different boards on this forum for different topics.

The Tube Amp Building - Tweaks - Repairs board is where you can post amp questions.

That board is listed here.
https://el34world.com/Forum/index.php?board=13.0

Thanks,
Doug Hoffman

68

Introduce Yourself / Thanks for your service!

« Last post by Goreng on October 19, 2025, 03:11:01 pm »

Hey Hey,

Thank you EL34 for keeping this place up, thanks to the regulars and moderators for sharing your knowledge.   

I've been utilizing this treasure trove of knowledge and opinions since its inception.  First amp I built used Hoffman Amps as a source of goods over 20 years ago, good times (turns out a 50watt Marshall plexi into a 2x12 is not appreciated by neighbors, nor a good place to start learning tube circuits).  Every 5 or so years I get an overwhelming urge to build a new amp.  Sometimes they turn out like what I envisioned, sometimes not.  Either way I come out the other side with more knowledge.  Currently playing through a amp based on a fender 5e9 circuit (tremolux) for blues, and have been going through iterations of a high gain SE amp (seeking a tone and almost done at this point, a couple of concerns) and have plans for my take on a BFDR.

If not messing with high voltage you can likely find me enjoying a bit of wind in the face on a 350excf or an old 81' Yamaha 250 Exciter.   I tinker, tweak or repair those types of machines as well. 

Please everyone, give yourselves a high five!
Thanks and cheers  ,
Goreng

69

Tube Amp Building - Tweaks - Repairs / Re: Bucking Transformer wiring

« Last post by Bash on October 19, 2025, 02:30:32 pm »

Hi, is some time ago but wondering if you fixed this issue? i run over same problem with an old Yamaha JA1701 which as you give him power just stuck at higher speed. I suspect some diodes might be the issue. I have other units that work perfect with switching from slow to fast speed.

Any info will be appreciated thanks

I couldn't figure it out myself, so I brought it to a local guy who is specialized in repairing all kinds of electronics.
If I recall correctly he replaced a few diodes and resistors. Now it works again as it should.

Not much help to you I guess...

70

Other Topics / Re: Meme of the day

« Last post by shooter on October 19, 2025, 02:26:50 pm »

...