Hey Dana, OT transformer primary choices

[skyboltone]

Dana:
You wrote in another thread:
"I would build it exactly like the liverpool (Front end, PI and PA). 8k tranny would work fine but I think if you went with a 10k it might even be a little closer to sounding and playing like a Liverpool. I have heard a liverpool played at 1/2 power (2 x tubes) and it still sounded great! I don't think you'll ever get the Marshall 18watt PI and power amp values to sound like a wreck. Just my 2 cents"

I have a couple of 10500 ohm 6V6 OTs out of Hammond organ AO-49 amps. I had planned on doing a 6v6 express (like Kelly's A1b) using that iron. What is it in particular that you will gain using that sort of PP load on 6BQ5's? Maybe my iron is better spent on a Liverpool.

Thanks in advance for the reply
Dan H

[Noel Grassy]

Skyboltone, I also have at least one of those, does your thoughts re: Liverpool build utilize four output tubes or two? It'd be great to get those old xfmrs honkin'? Their former life never hinted at such posibilities.

[skyboltone]

Skyboltone, I also have at least one of those, does your thoughts re: Liverpool build utilize four output tubes or two? It'd be great to get those old xfmrs honkin'? Their former life never hinted at such posibilities.

Well, I can't imagine 10500 on parallel 6V6s so no, just a pair. I been farting around with an AO-35 (8500 primary OT w/EL-84s) inside the original chassis for awhile. I got it sorta nice but it's got a way to go before I'll turn it over to my son. Right now it's got a 1/2 12AX7 stage, followed by a Leo Fender single nob tone/volume control, followed by a 100K/10K second triode stage with no cathode cap, into a long tailed 12AU7.

Next I'm gonna try to parallel the first AX7, use 1/2 a second one in the no cathode cap configuration, followed by a cathodyne PI and then on to the EL-84s. Who knows where it all leads. I'm learnin' stuff too.

[UR12]

Dana:
You wrote in another thread:
"I would build it exactly like the liverpool (Front end, PI and PA). 8k tranny would work fine but I think if you went with a 10k it might even be a little closer to sounding and playing like a Liverpool. I have heard a liverpool played at 1/2 power (2 x tubes) and it still sounded great! I don't think you'll ever get the Marshall 18watt PI and power amp values to sound like a wreck. Just my 2 cents"

I have a couple of 10500 ohm 6V6 OTs out of Hammond organ AO-49 amps. I had planned on doing a 6v6 express (like Kelly's A1b) using that iron. What is it in particular that you will gain using that sort of PP load on 6BQ5's? Maybe my iron is better spent on a Liverpool.

Thanks in advance for the reply
Dan H

I just thought that would be a good starting point for comparison between the original Liverpool (4 El84's running 5.2K) and the 15 watt version with only 2 El84s running at 10.4k. You will gain having the same matching impedance that you had on 4 tubes so in theory if we keep the proportions the same. Your plate load doubles when going to 2 tubes so why not match that with the proportional increase in primary impedance, all other things staying the same (Bias, Plate and screen voltages). You could also run a 5.2k tranny and lable the 4/8/16 ohm secondaries to 8/16/32 ohms. Either way should couple the same amount of power and frequencey response as the original 5.2k and 4 El84s had. I think I would stick with a 5.2k or 6.6k with the 6v6s for a Express style amp.

[novosibir]

Next I'm gonna try to parallel the first AX7, use 1/2 a second one in the no cathode cap configuration, followed by a cathodyne PI and then on to the EL-84s. Who knows where it all leads. I'm learnin' stuff too.

I've tried this in my amp builds - Dr. Z does it (at least in some amp models), Vic does it in the Mojave Peacemaker...

... but I always went back to a single triode. I found, that a single triode is sounding more organic, whereas a doubled triode is too much pronouncing the higher mids - it's too much 'into your face' IMO.

Also read this:

http://members.aol.com/sbench102/dax7.html

Larry

[skyboltone]

I just thought that would be a good starting point for comparison between the original Liverpool (4 El84's running 5.2K) and the 15 watt version with only 2 El84s running at 10.4k. You will gain having the same matching impedance that you had on 4 tubes so in theory if we keep the proportions the same. Your plate load doubles when going to 2 tubes so why not match that with the proportional increase in primary impedance, all other things staying the same (Bias, Plate and screen voltages). You could also run a 5.2k tranny and lable the 4/8/16 ohm secondaries to 8/16/32 ohms. Either way should couple the same amount of power and frequencey response as the original 5.2k and 4 El84s had. I think I would stick with a 5.2k or 6.6k with the 6v6s for a Express style amp.

Ok, thanks. I get it. The Hammond Amps are odd in that they use 368-0-368 (at 117) for the PS and 10500 on the OT with 6V6s. In the AO-35 they use 290-0-290 on the PT and 8500 on the OT with EL-84s. The OT in both cases is definitely a 20 watt max size. The PTs are huge though, I've put 230MA on one for two hours with no appreciable heating. I'm so cheap I'm gonna use this stuff on something, one way or another. Zener the center tap and redesign the bias supply etc. I have a Fisher 6600 OT for the express build. From my reading here I think that 6.6K is the preferred OT for these, true?

And Larry, thanks for the distortion analysis information. I've copied it to file and will study it some more as I work out the details of this little amp. It's definitely not well balanced tonally in it's current iteration, but I have more ideas to try.

Dan H

[harryk]

Hi guys! Because I got my Liverpool 2xEL84 project to the phase where it is only missing a cab, I can start to think my next Twreck project. I am somehow stuck mentally with it`s design and philosofy. I would like to do now original Express with 6V6 tubes. My question is: What are spesifications for PT? What are needed secondary voltages - is it 2x260V to get it right? A help here is much appreciated. Regards Harry

[skyboltone]

Hi guys! Because I got my Liverpool 2xEL84 project to the phase where it is only missing a cab, I can start to think my next Twreck project. I am somehow stuck mentally with it`s design and philosofy. I would like to do now original Express with 6V6 tubes. My question is: What are spesifications for PT? What are needed secondary voltages - is it 2x260V to get it right? A help here is much appreciated. Regards Harry

Well, the Kelly and Francesca scheme shows 585, or 292.5-0-292.5. But Dana talks about using lower voltages so he's the man here I think.

[UR12]

I'm so cheap I'm gonna use this stuff on something, one way or another. Zener the center tap and redesign the bias supply etc. I have a Fisher 6600 OT for the express build. From my reading here I think that 6.6K is the preferred OT for these, true?


Dan H

I would use it also, free or otherwise. Granted they may not have the same stack size, the same type of steel, the same interleaves , etc, etc but you really don't know what they are going to sound like until you try them. I used a OT in my Junkyard Express that I knew nothing about except that it came out of an amp that was running 2 x EL34s. Turned out that it worked so well that we had a hell of a time trying to figure out why it sounded better than the rest we tried. Sometimes you just got to go with what you have on the shelf and if it works then great, and if it don't, then try something else. I think that you really need to listen to both the 5.2k and the 6.6k and determine what sounds good to you. The difference is subtle and not night and day. You get a little more responsiveness and bite at 5.2K and the 6.6k rolls off a little of the bite but is not as responsive. That doesn't mean that a 6.6k isn't responsive or or th 5.2k lets the amp breakup earlier on the VOL knob. You just got to try it and see what sounds good and responds to your ears and axe. You might want to go one way for a Strat and the other for a LP.

That's a good one Fisher OT in a Fisher TW That has to be the Perfered way to go.

Hi guys! Because I got my Liverpool 2xEL84 project to the phase where it is only missing a cab, I can start to think my next Twreck project. I am somehow stuck mentally with it`s design and philosofy. I would like to do now original Express with 6V6 tubes. My question is: What are spesifications for PT? What are needed secondary voltages - is it 2x260V to get it right? A help here is much appreciated. Regards Harry

No, I would go with a 300-0-300 just like the Express. The Express sounds great with 6V6s. I would also use a fixed bias and supply like the Express.

[harryk]

Thanks Dana of your help. My fingers are burning to do one real Express for myself. I am quite sure that there will be troubles on the building way, but with you here in this forum life is little easier in Twreck Wonderland. Harry