some odd tubes

[menger]

i got some odd tubes resently , 7868 7591 dont realy know what to do with them. 7868 are 9 pin someone said there alot like a el84 and easy to drive to distort i was thinking theyed make a nice 36 watt type build. anyone used them they came with tranys and a odd recto 5bc3. wouldnt mind basing a build on these tubes but may never get new tubes if they go. anyone built with these. what amps maybe help point me in a dirrection mark"menger"enger

[Alexo]

Hi Mark. 7868's and 7591's are basically the same tubes, but in different bottles - the 7591's use octal bases while the 7868's use magnovals.

These are very nice tubes, they came out towards the end of the (first) golden age of tube audio, and they represent some refinement over earlier designs.

They have a very smooth and musical sound, they're capable of a lot of power in a small bottle - up to 45 watts from one pair in push-pull - and they are in fact very easy to drive, just like an EL84. You can definitely use a pair to build a 36 watter, obviously, it'll sound different from an amp built with EL84's, but it will sound good and have a similar overdrive threshold.

The datasheets for these tubes list several example circuits, and there has been discussion on them here if you search around. Not a lot of guitar amps have been built with them though, check out some old Ampeg schematics, like the Reverborocket, etc..

[menger]

thanks alexo i may do a tmb 36 and maybe a voxy se theyed make some sweet se real load im sure i got them out a hammond organ it ran 4 el84 and a pair of 7591 with three different opts so ive got a ton of options on this one. and i got 4 5ar4/gz34 so i got lots of planning some bugle boy preamp tubes also she was a buet i realy didnt want to tear it up but they were giving it away

[Brucer]

Some of the Bogen tube PA amps use the 7868 tubes. I think the CHB20. CHB35, CHB50 and CHB100 amps all used the 7868 as power tubes. Bogen seemed to be big on noval tubes. In my CHB14, though, they went with ECL86 (combo triode/pentode -- PI and power) tubes with an EF94/6AU6. a septal tube, as the pre-amp. Most of them used EZ80 and EZ81 tubes as the rectifier, I think. My CHB14 uses an EZ80.

I've heard a couple of "revived" and re-voiced Bogen tube amps (CHB35 and CHB50?) that sounded great as guitar amps.

So, yeah, the 7868 tubes are great tubes. They're probably going to be hard to find at some point and I think they bring a premium, already.