Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mats on November 11, 2016, 01:15:06 pm

Title: Univox amp
Post by: Mats on November 11, 2016, 01:15:06 pm

Hi
I talked to a friend the other day, he wants some input to start build one small amp with tremolo.
At first we talked about SE amps but then we got into PP amps and looked at one Univox U-45B (four tube amp) on the Youtube.
It was then that I looked at some information about another Univox amp, the U-75.
Looks like its a five tube amp (12AX7, 12AX7, 6AQ5, 6AQ5 and 6X4)
I cant find any more info or schematic of this amp. Some direct to U-155R, but its not the same preamp tubes.
Does anyone have a schematic of U-75 ?
/Mats

Title: Re: Univox amp
Post by: uki on November 13, 2016, 09:34:39 am

Here is a small amp with tremolo with good information about it!

http://sluckeyamps.com/RCA/Ampeg_J12B.pdf (http://sluckeyamps.com/RCA/Ampeg_J12B.pdf)
http://sluckeyamps.com/RCA/RCA.htm (http://sluckeyamps.com/RCA/RCA.htm)
https://www.youtube.com/watch?v=Kfqidpvr2hI (https://www.youtube.com/watch?v=Kfqidpvr2hI)

Title: Re: Univox amp
Post by: Mats on November 13, 2016, 12:19:21 pm

Hi
Thank you for your answer and information about the Ampeg Jet.


I will try to search for more info. about the U-75.
Perhaps the U-75, is like the U-45B  and that they changed 6BM8 tubes for 6AQ5, 6AQ5 and one 12AX7
/Mats

Title: Re: Univox amp
Post by: silverfox on November 13, 2016, 01:44:59 pm

One research hit indicates it's the same as this amp without the Reverb.

http://el34world.com/charts/Schematics/files/univox/Univox_U-155R_GUITAR_AMP.pdf (http://el34world.com/charts/Schematics/files/univox/Univox_U-155R_GUITAR_AMP.pdf)

silverfox.

Title: Re: Univox amp
Post by: kagliostro on November 13, 2016, 02:57:32 pm

But in the 155 there is a 6AU6 as V1 .....


Franco

Title: Re: Univox amp
Post by: silverfox on November 13, 2016, 05:42:39 pm

An EF86 or 5751 may work in that position as a substitute. Matchless DC30 channel 2 input example.

silverfox.

Title: Re: Univox amp
Post by: Ritchie200 on November 14, 2016, 02:45:36 pm

The U75 is certainly a mystery as it appears nobody has any schematics or has bothered to share their drawings.  Here is a gut shot with some components in view.  Might get you started...


https://reverb.com/item/2324654-univox-u-75-2x10-tube-combo-1966-black-blue-jensen-c10-s


Jim

Title: Re: Univox amp
Post by: kagliostro on November 14, 2016, 04:44:50 pm

Here is the photo of the board (is not possible to save imeges from the link)

(http://i.imgur.com/S1OKNJP.jpg)

and here of the faceplate

(http://i.imgur.com/iePGSzU.jpg)

Seems that someone swapped some nice Paper Oil capacitors for polietilene .....

(http://i.imgur.com/o12DRIl.jpg)

Franco

Title: Re: Univox amp
Post by: jjasilli on November 14, 2016, 06:26:55 pm

Here's a U45 I did a trem repair on, with schematic.

Title: Re: Univox amp
Post by: 2deaf on November 14, 2016, 10:16:02 pm

With the tube lineup, it might be more similar to the U-255R without the reverb.  I rebuilt one that was very similar to a U-255R and Fenderized it as long as I was at it.  The only ID on the whole amp was "MUSCAL (sic) AMPLIFIER MODEL G" on the printed circuit board.  The lack of model ID's on Univox's makes me wonder how people know what model they have.

Title: Re: Univox amp
Post by: Mats on November 15, 2016, 11:59:27 am

Hi
Thanks for your effort, in finding some information about the U-75.
/Mats

Title: Re: Univox amp
Post by: jjasilli on November 15, 2016, 01:56:23 pm

Here's the Prowess sight with more schematics.  I could not find it yesterday  (thought it was "Powers"; it's "Prowess"):  http://www.prowessamplifiers.com/schematics/univox/ (http://www.prowessamplifiers.com/schematics/univox/)

Title: Re: Univox amp
Post by: JRobin68 on January 23, 2022, 09:37:36 pm

Quote from: Mats on November 11, 2016, 01:15:06 pm

Hi
I talked to a friend the other day, he wants some input to start build one small amp with tremolo.
At first we talked about SE amps but then we got into PP amps and looked at one Univox U-45B (four tube amp) on the Youtube.
It was then that I looked at some information about another Univox amp, the U-75.
Looks like its a five tube amp (12AX7, 12AX7, 6AQ5, 6AQ5 and 6X4)
I cant find any more info or schematic of this amp. Some direct to U-155R, but its not the same preamp tubes.
Does anyone have a schematic of U-75 ?
/Mats

Title: Re: Univox amp
Post by: JRobin68 on August 10, 2022, 05:05:27 am

This is the U75 schematic

Title: Re: Univox amp
Post by: kagliostro on August 10, 2022, 07:47:26 am

(https://el34world.com/Forum/index.php?action=dlattach;topic=21091.0;attach=99958;image)

Really nothing in good shape but very easily readable

Have you a way to post that schematic positioned in plan (flat) ?

THANKS

Franco

Title: Re: Univox amp
Post by: PRR on August 10, 2022, 11:40:48 am

Quote from: kagliostro on August 10, 2022, 07:47:26 am

Have you a way to post that schematic positioned in plan (flat) ?

I think he copied it off an auction site, does not have the actual paper?

It is ugly but readable.

I did some editing but it really needs the old brown image to check small details.

Title: Re: Univox amp
Post by: JRobin68 on August 10, 2022, 01:35:08 pm

It's all I have, took forever to even find that one.

Title: Re: Univox amp
Post by: sluckey on August 10, 2022, 01:52:28 pm

It's already in Hoffman's schematic library.

     https://el34world.com/charts/Schematics/files/Univox/Univox_U75.pdf

Title: Re: Univox amp
Post by: JRobin68 on August 10, 2022, 02:18:47 pm

Nothing like getting a 6yr. Old thread started again, lol.

Title: Re: Univox amp
Post by: kagliostro on August 10, 2022, 04:01:08 pm

Thanks to all


Franco