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 #113137  by Smolder
 Thu Apr 26, 2012 7:45 am
I've been doing some research. Since these are available cheap, it might be great for this community to have an ongoing conversation about how to best mod/utilize them.

I purchased a working twin chassis for an empty head cab I have. The description was late 70's, so its likely that it will come with ultra linear set up. I have a couple of UL amps (Dr Z's) that really sound great, so I am optimistic. There was a note on a thread about a tech that did a nice conversion... so I'm researching.

It looks like for the most part the preamp section remains consistent with previous, though I haven't been able to print out schematics and do a component-to-component examination. I wouldn't think the full wave rectifier configuration would have much effect on tone. What I do see (and read) is that the power tube grids are powered directly from the OT... sort of a negative feedback system. The common wisdom on the inter web recommends disconnecting or adding a variable resistor (pot) to the traditional negative feedback loop.

I would think that the extra clean of the UL configuration, would in general, play into the Jerry tone. But I haven't played through one... so I'll have to wait and see.

Any input or comments would be greatly appreciated.
 #113144  by Smolder
 Thu Apr 26, 2012 9:20 am
Wow... How'd I miss that. Thanks for the link.

I have two twins I run with only two tubes... Works great. Neither are UL.
 #113147  by Tennessee Jedi
 Thu Apr 26, 2012 9:36 am
Smolder wrote:Wow... How'd I miss that. Thanks for the link.

I have two twins I run with only two tubes... Works great. Neither are UL.
Yeah ... thats what I want to try .... not sure how to go about it , though ....
I do LOVE the Amp though .... sounds great to my ears ... just too damn loud ...
Image
:-)
 #113174  by Tony6Strings
 Thu Apr 26, 2012 3:02 pm
I have an ultralinear Pro Reverb, 70 watt. It's one of the best sounding amps around. I'm big on clean headroom, so 135w sounds like a dream come true to me...
 #113179  by hippieguy1954
 Thu Apr 26, 2012 3:48 pm
Tony6Strings wrote:I have an ultralinear Pro Reverb, 70 watt. It's one of the best sounding amps around. I'm big on clean headroom, so 135w sounds like a dream come true to me...
I have a '79 ultra 135 watt for sale in Garage Sale. forum/viewtopic.php?f=334&t=12159&p=112 ... in#p112862

They are fantastic amps, just too heavy for me these days! :smile: :smile: :smile:
 #113195  by Smolder
 Fri Apr 27, 2012 6:38 am
Tennessee Jedi wrote:Yeah ... thats what I want to try .... not sure how to go about it , though ....
I do LOVE the Amp though .... sounds great to my ears ... just too damn loud ...
nice rig.

all i did was to take out the outer or inner two tubes and check/adjust the bias. I also put a pull pot on the trem intensity... so that it can be pulled out of the circuit. it gives just a bit more gin/hair at lower volume. the other thing i'm toying with is a brakelite attenuator to tame some of the volume. you might also try a 12ax7/12ay7/12at7/5751/12au7 in the phase inverter slot for less gain there.

https://www.kcanostubes.com/content/pre ... lity-guide

i see nothing on the UL twin schematic to make me think that it wouldn't work... and have read in other forums that it's recommended, but ill defer to 'tea;' techs and those who have actually done it with a UL twin.
 #113201  by hippieguy1954
 Fri Apr 27, 2012 8:38 am
I always played mine at 3 or 4. Master volume on 10. I guess I'm just used to louD!

You can remove one of each pair of the power tubes, but I'm pretty sure you have to disconnect one speaker to maintain the correct ohms. After reading the posts in the links below, seems to me you do not have to disconnect one speaker because the amp can take it and by not disconnecting one speaker it will lower the volume more!

http://blindman.15.forumer.com/a/fender ... 30433.html

http://www.premierguitar.com/Magazine/I ... iques.aspx

http://www.thegearpage.net/board/archiv ... 74077.html

You might want to think about consolidating these two Ultralinear threads. :roll: :smile: :smile: :smile:
 #113214  by Smolder
 Fri Apr 27, 2012 12:13 pm
Thanks for the reminder hippieguy... I'm running only a single JBL in mine for an 8 ohm load that matches the transformer with two power tubes removed.

I am also playing with a super reverb. I've got a emplacement 4/8 output transformer with a 16 ohm, 15" original cone JBL D-130. That combination is really really great.
 #113216  by hippieguy1954
 Fri Apr 27, 2012 12:32 pm
Smolder wrote:Thanks for the reminder hippieguy... I'm running only a single JBL in mine for an 8 ohm load that matches the transformer with two power tubes removed.

I am also playing with a super reverb. I've got a emplacement 4/8 output transformer with a 16 ohm, 15" original cone JBL D-130. That combination is really really great.
Great, man! I'm glad it's working out! :smile: :smile: :smile:
 #113277  by Smolder
 Sat Apr 28, 2012 9:08 pm
turns out the chassis I bought, though being a '77, is not an ultra linear. But I'm still very curious how to make them sing.
 #113280  by Tony6Strings
 Sun Apr 29, 2012 2:03 am
Smolder wrote:turns out the chassis I bought, though being a '77, is not an ultra linear. But I'm still very curious how to make them sing.
Crank that sucker up to about 6, and hit it with a clean boost. It'll sing.