Twin reverb 135w With vintage output Transformer.

[Aoxomoxoa710]

Hello. I'm new in the group. Can someone help me with my twin reverb 135w ultralinear?

The output transformer has broken.

I have an output transformer from an older twin reverb. Exactly a 022889. It is not an ultralinear output transformer. It does not have 4 wires that go to the power tubes. It only has two wires. I have put this output transformer in the amplifier and it seems to work perfectly. My question is. Do I have to modify something in the circuit of my amplifier. Change some value or add some resistance? Any information is appreciated.Thanks.

 

[Ten Over]

Hello. I'm new in the group. Can someone help me with my twin reverb 135w ultralinear?

The output transformer has broken.

I have an output transformer from an older twin reverb. Exactly a 022889. It is not an ultralinear output transformer. It does not have 4 wires that go to the power tubes. It only has two wires. I have put this output transformer in the amplifier and it seems to work perfectly. My question is. Do I have to modify something in the circuit of my amplifier. Change some value or add some resistance? Any information is appreciated.Thanks.

How did you wire the screen grids?

 

[Pete Farrington]

The valves will be in a happier place with the correct OT.

 

[Aoxomoxoa710]

Hello. Thanks for the answers. The two cables of the output transformer are connected to each pair of 6L6. They are connected in the classic way of non-ultralinear twin reverbs of 85w or 100w. For the rest the only modification is the output of the speakers that are wired in the manner of non-ultralinear amplifiers. Only speaker output, no exterior speaker wiring, no line output. The amp sounds good and the bias is not bad with a 40k resistor.About 39ma bias with Tad 6L6Gc- Str quartet. So you recommend that I buy an Ultralinear output transformer? Could I sell my non-Ultralinear twin reverb transformer from the late 60s and buy a new one.The 022889 output transformers are appreciated. I was just wondering if I could keep this transformer and maybe make some modification. I have read in this forum (Jon Snell explains it and publish several photos, thanks Jon,and I add these diagrams photos in this publication) that some people do not want to connect the two ultralinear cables and Remove and insulate both Yell/Brown and Yell/Blue wires from the transformer. then Connect the cold end of the 2k7 10W resistor (as shown in the pictures) to where the Yell/Brown and Yell/Blue wires used to go. But I don't know if this is the right way for me. I don't have an Ultralinear output transformer that I can use suppress Yell/Brown and Yell/Blue wires. I have another story.I have a non-ultralinear output transformer. Probably 85w or 100w. I also don't know if the impedance is 8ohm or 4ohm. This doesn't worry me, at the volume I play this is not a problem for the amp.The amp sounds good.So I have three options.1 leave it as is.2 change the output transformer or 3 make the modification that was suggested in another post (attached photo).I also put a photo of my output transformer.Many Thank you all for keeping these posts alive and to the vintage amp lovers for keeping them alive for many years.

 

[Pete Farrington]

then Connect the cold end of the 2k7 10W resistor (as shown in the pictures) to where the Yell/Brown and Yell/Blue wires used to go

As you've done that and are happy with the results, then that should be ok. It's possible that the 2k7 10W may overheat if the power amp is overdriven hard, but as you're not using it like that then it should be fine.

Ideally the amp should be repaired such that it worked as its designer intended, but if you're happy then there's no benefit to you in spending more money and time in doing that.

 

[Aoxomoxoa710]

thank you very much Pete. Currently the cold end of the 2k7 10W resistor is not connected where the Yell/Brown and Yell/Blue cables should go. I don't understand very well. may overheat if 2k7 10W is connected?or may overheat if 2k7 10W is not connected to tubes?Thank you very much again.

 

[Pete Farrington]

Currently the cold end of the 2k7 10W resistor is not connected where the Yell/Brown and Yell/Blue cables should go.

So where have you taken the feed for the screen grids (pin 6) from?
eg the OT CT, pin 3 of the same socket.

 

[Aoxomoxoa710]

You're right, Pete. I'm not a technician and sometimes I don't understand things well. The blue and brown OT cables go to pin 3 of each pair of tubes.What I haven't connected pin 6 with 2k7 10W in the part where the white cables are as Jon Snell said in another publication. My apologies if I have not explained myself well. Thank you.

 

[Pete Farrington]

I have put this output transformer in the amplifier and it seems to work perfectly.

So currently, where have you taken the feed for the screen grids (pin 6) from?
eg the OT CT, pin 3 of the same socket.

 

[Aoxomoxoa710]

The best idea is to open the amp again and take a photo. Maybe I'm missing something that I don't remember about how exactly the output transformer is connected. I'm going to open the amp again and post a photo. Thank you very much

 

[Aoxomoxoa710]

Right, what you had told me is correct. Blue / brown cables go to pin 3. All pin 6 are connected to each other and connected to 2k7 10W. My question is if pin 6 is connected to the correct side of the resistor. Pin 6 is connected next to the red wire. Should it be connected to the 2k7 10w side where the two white wires are? Maybe my question does not make sense and is very non-technical, but I already said that I am not a specialized technician, just a newbie who wants My amp runs as safely as possible. Thanks Pete and Ten Over for sharing all yours knowledge.

 

[Pete Farrington]

My question is if pin 6 is connected to the correct side of the resistor. Pin 6 is connected next to the red wire. Should it be connected to the 2k7 10w side where the two white wires are?

Going from the documentation @Ten Over kindly provided in post 2, I think it would be beneficial if the feed was taken from the other end, white wires, not red wires end.
It'll be the lower voltage end.
Doing that will reduce the anode current, both at idle (slightly) and at high power output. The latter will help to protect the valves against overheating when the amp is pushing out audio power.

 

[Aoxomoxoa710]

Thank you very much Pete. I'm going to try that configuration. Thanks again!

 

[Aoxomoxoa710]

Thanks Pete.My amp was running on the hot side for many years. I started thinking about this when changing tubes and adjusting the bias. Connecting pin 6 on the white wires side of 2k7 10W has been the decisive change. the amp It was connected to the red wires side of 2K7 10w.Of course the amp needed a bias adjustment. At first I put a 33k resistor which is the stock value for UL but very cold.My transformer has less watts than UL transformer, so I went closer to 27k resistor which is the value of the regular Twin Reverb. Finally my choice has been 22k for 37 mA bias. The amp has a more adjustable eq and better sound. So many thanks to @Ten Over for the schematics. @Jon Snell who published in another post how to change ultralinear OT to Linear OT in 135w UL and to @Pete Farrington who has clearly explained the way to go. Thanks to everyone who has responded to the post.