Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: LooseChange on August 18, 2018, 09:14:50 am

Title: Hoffman 30 watt amps on the bench
Post by: LooseChange on August 18, 2018, 09:14:50 am

Hi Guys!


I know I've been absent for quite some time but I got to share what's on my bench...


Building and Repairing... Life is good.

Title: Re: Hoffman 30 watt amps on the bench
Post by: uki on August 18, 2018, 10:49:32 am

Beautiful amp!! What are the PA tubes?

Title: Re: Hoffman 30 watt amps on the bench
Post by: LooseChange on August 18, 2018, 11:24:53 am

EL84's.
Here's the circuit....
https://el34world.com/Hoffman/images/2El84skem.gif

Title: Re: Hoffman 30 watt amps on the bench
Post by: ginger on August 18, 2018, 12:09:36 pm

And the complaint ?

Title: Re: Hoffman 30 watt amps on the bench
Post by: LooseChange on August 18, 2018, 01:38:17 pm

Came in for general maintenance and a small mod reversal.

Title: Re: Hoffman 30 watt amps on the bench
Post by: jjasilli on August 18, 2018, 07:03:11 pm

 :thumbsup:

Title: Re: Hoffman 30 watt amps on the bench
Post by: EL34 on August 19, 2018, 02:02:44 pm

A blast from my past
They look good

Title: Re: Hoffman 30 watt amps on the bench
Post by: DummyLoad on August 19, 2018, 06:47:58 pm

how are those even making 30W with a pair of EL84?


--pete

Title: Re: Hoffman 30 watt amps on the bench
Post by: sluckey on August 19, 2018, 07:10:51 pm

Looks like some of the early ones actually used EL34s...
(https://el34world.com/Hoffman/images/IN-54.jpg)

And on the layout the text says EL84s but the octal sockets are wired for EL34s...
(https://el34world.com/Hoffman/images/El84skem.jpg)

Title: Re: Hoffman 30 watt amps on the bench
Post by: EL34 on August 20, 2018, 07:21:51 am

Quote from: DummyLoad on August 19, 2018, 06:47:58 pm

how are those even making 30W with a pair of EL84?
--pete

Fake name, just to draw in the crowds  :icon_biggrin:

Title: Re: Hoffman 30 watt amps on the bench
Post by: EL34 on August 20, 2018, 07:25:56 am

Quote from: sluckey on August 19, 2018, 07:10:51 pm

Looks like some of the early ones actually used EL34s...

And on the layout the text says EL84s but the octal sockets are wired for EL34s...

The top picture is inside one of the 50 watters
Not sure what the layout is all about
Looks like it was copied over from a 50 watter and then labelled wrong
I'll have a look through some of the old documents to see if I can find the EL84 layout

Title: Re: Hoffman 30 watt amps on the bench
Post by: EL34 on August 20, 2018, 07:38:36 am

Looks like I made some with 6v6's
I found these drawings on the library page
I do not even remember the 6V6 versions
One with DC heaters and one with AC heaters
And the el84 version also

(https://el34world.com/Hoffman/images/26V6skemdc.gif)

(https://el34world.com/Hoffman/images/26v6skem.gif)

(https://el34world.com/Hoffman/images/2El84skem.gif)

Title: Re: Hoffman 30 watt amps on the bench
Post by: EL34 on August 20, 2018, 07:47:31 am

Quote from: sluckey on August 19, 2018, 07:10:51 pm

Looks like some of the early ones actually used EL34s...
And on the layout the text says EL84s but the octal sockets are wired for EL34s...

Hey Steve, where did you find that image?
I don't see it linked on the library page

Title: Re: Hoffman 30 watt amps on the bench
Post by: sluckey on August 20, 2018, 10:02:11 am

It's way down a rabbit hole!  :icon_biggrin:

Look way down near the end of the library page. There's a section called "Hoffman Amplifiers stuff" and a sub section called "Photo pages". Click on the first link called "The original Hoffman 30 watt head" which leads to this page...

     https://el34world.com/Hoffman/Original30.htm

Finally click on the last thumbnail (bottom/right) to get that pic. I thought 30 watts was a realistic power for a push/pull cathode biased EL34s. So, are those really 6V6s?

Title: Re: Hoffman 30 watt amps on the bench
Post by: EL34 on August 20, 2018, 10:08:00 am

Ok, I found it
I'll add the 6v6 and el84 layouts to that page

I have a bunch of customers images that were sent to my over the years
I'll upload all that stuff just for history

Title: Re: Hoffman 30 watt amps on the bench
Post by: shooter on August 20, 2018, 12:09:25 pm

Quote

are those really 6V6s?

my money is on 6L6's running hot, although my '34 pp self biased does run ~~30W

Title: Re: Hoffman 30 watt amps on the bench
Post by: EL34 on August 20, 2018, 02:06:42 pm

Over the years, I have been collecting customer images when they send them to me
I uploaded a bunch of customer images of the H30 heads

There was even one that was a special order and was built into one of the metal 50 watt chassis
Powder coated in gray speckle
It looks pretty cool

Here's the images page
https://el34world.com/Hoffman/Original30.htm

Here's all the layouts I could find for those amps
https://el34world.com/Hoffman/Original30layout.htm

Title: Re: Hoffman 30 watt amps on the bench
Post by: shooter on August 20, 2018, 04:24:20 pm

Steve's image through me for a minute, couldn't understand why you used all dual-ganged pots  :think1:

Title: Re: Hoffman 30 watt amps on the bench
Post by: EL34 on August 20, 2018, 05:25:44 pm

Quote from: shooter on August 20, 2018, 04:24:20 pm

Steve's image through me for a minute, couldn't understand why you used all dual-ganged pots  :think1:

Haa, I see it now
reflections in the plexi