KT-66, 7591, 5881 Express or Rocket etc.

[skyboltone]

I've got some iron. Hammond Organ Iron. OT 8800/8. My OEM power transformers are rated (As Phil at Heyboer said) over 200 ma and 240-0-240. I think the PT will run a pair of 5881s at 4400/4 without strain. Or maybe 4 6V6s? Anyway, many of you have played with KT-66, EL-34 and 7591s. Will these tubes perform at 330VDC? I think the 5881 will but I do want lots of sparkle. (Maybe just run a bluedog and a G12-65?)

The Hammond Organ setup (AO-68 ) used 375VAC into a 5AR4 (cap input) and the 7591s. The PT measures 81 ohms across the HT coil; end to end. Probably that might be a good way to go but I hate fragile tubes and I don't want to have to buy a dozen pairs just to be safe. Also, I've foound JJ to be prettty reliable on other tubes so if I go 5791s I'll probably go that route.

Any and all suggestions, unkind words, general drivel, and instruction is welcome.

Dan

[dave g]

I am running a quartet of JJ 7591s in my old Fisher stereo I keep here at college, and my experiences have been positive. I have no idea what they would sound like in a guitar amp - I know they do have a different pinout than most other octal types. I'd say it's worth a try.

[skyboltone]

I am running a quartet of JJ 7591s in my old Fisher stereo I keep here at college, and my experiences have been positive. I have no idea what they would sound like in a guitar amp - I know they do have a different pinout than most other octal types. I'd say it's worth a try.

Thanks Dave. I just ran the numbers for a pair of EL-34s in a Rocket layout with a 5U4 rectifier and the Plates will run at about 430 at idle and drop to 405 or so at 185 on the plates and 15 or so on the screens so, should make for an interesting project with the original Hammond Organ iron PT and OT. I just can't leave well enough alone. An Express Rocket. No doubt the PT will sag big time at full roar when the screens glow like a toaster. May not roar at all.......may kinda whimper.

I'm kinda envious of the Fisher 500. Do you happen to know what fisher used for a plate voltage on the 5791? I've got an old Harmon Kardon reciever that runs 6V6s that needs re-capping. I intend to get it going when the rain starts.

[doctord02]

Different Dave, different Fisher - X101B - but same tubes...

I had Paul Ruby repair mine that had a blown PT - turns out the PT is remarkably similar to a JTM45 PT, so thats what we replaced it with, a Heyboer power tranny for a Marshall JTM45 - the end bells even fit correctly... 350-0-350 - gives about 450 after rectification (GZ34) and under a load...

[dave g]

Actually, mine is an X101B as well

It used to belong to my dad from his college days. I found it buried in my garage a couple years back; still had all the original tubes, transformers, and caps. I toyed with the idea for a while of gutting it and using the iron to build a couple guitar amps (since those two OTs look oh so tempting), but in the end decided it was better to restore it.

I did, however, swap in EH preamp tubes and remove the Fisher labeled Telefunkens that were in there...they ended up in a couple Wrecks

[skyboltone]

Actually, mine is an X101B as well
(since those two OTs look oh so tempting), but in the end decided it was better to restore it.

I bought a pair of those OTs a few years ago. One was dead, dead, and the other one is fine. 6600/4,8,16. I've been saving it for a Wreck but am too cheap (lots of other projects) to buy the proper 300ma power transformer. It will get used for a personal amp at some stage.

[stubbyfex]

Hello!
I like the sound of the 7591 tubes. They have been called a 6L6 in a small bottle. Ampeg made many models with them, the Jet, the Reverbarocket and several others. I've even seen a few Premier amps using them.

[RJ Guitars]

I've got some iron. Hammond Organ Iron. OT 8800/8. My OEM power transformers are rated (As Phil at Heyboer said) over 200 ma and 240-0-240. I think the PT will run a pair of 5881s at 4400/4 without strain. Or maybe 4 6V6s? Anyway, many of you have played with KT-66, EL-34 and 7591s. Will these tubes perform at 330VDC? I think the 5881 will but I do want lots of sparkle. (Maybe just run a bluedog and a G12-65?)...

Any and all suggestions, unkind words, general drivel, and instruction is welcome.

Dan

Dan,

The KT-66 Rocket tranny I'm using is a 245-0-245 250 mA. I get great tone and plenty of power (It's probably not that many watts) but after a point it's too stinkin' loud for me to turn it up any more and everybody is getting pretty annoyed with the nose levels...

Running KT-66's at that voltage yields a pretty early breakup (9:00) using the standard Rocket preamp and a humbucker. There is not an excess of clean headroom but plenty of volume to play with, and it does stay clean and bright if I roll the guitar down a few clicks.

rj

[skyboltone]

Thanks RJ. When Leo was doing all that inventing and copying back in the '50s he kept pushing the voltage up and up. And along with PA plates at higher voltages he kept pushing the gain at the same time. Wanted them amps to cut through the drums and the honky tonk noise where those old western swing bands played. There just ain't enough time to try all the different permutations of plate voltage and drive to get the right balance of headroom and grind. Ken went opposit Leo it seems. Running 6CA7s at 410 volts has got to be a record low. I think they just kept fussing with it till it sounded right.