Small OT

[Alf]

Does anyone know of atube that cab be used with a small OT ( 3 watts maybe) and has primary impedance of 2.5 K ( secondary is 8 ohm ).
I have looked but can;t seem to find a suitable tube.
Would an ECL 86 work ( it really needs 5 K ?) . What will happen if I use it with this xformer ?

Alf

[Jazz P Bass]

I am assuming single ended class A?
The ECL86 is a triode & a pentode.
So are we talking the pentode?
From what I can gather on the datasheet, the plate resistance is 10K.

[Chuck H]

FWIW you don't need to run that secondary into an 8 ohm load! You could run it into a 16 ohm load and reflect a 5k primary impedance. 16 ohms is a very limiting impedance for a "mini head" type amp, but since 16 ohm speakers aren't hard to come by you could make it a small combo with either a low Vp 6V6 or parallel the triodes on a 12au7 (close enough).

Or... Save it for a reverb drive transformer. Tanks are available with many impedances that could reflect an appropriate load on a driver tube with that OT.

[Alf]

Yes, we're talking single ended Class A. And you're right the plate load is 10 K. So that won't work
But they must have been used ( the penthode) for the poweramp part of probably an old taperecorder, I am fairly certain of that.
It would be very handy if there was an easy way to find out which tube works for a certain impedance an exel file or something.
And Chuck , that's a good suggestion , a 16 ohm load or a reverb xformer.
Does it mean that it would work with a 32 ohm load ( 2x 16 ohm in series) ?

Alf

Thanks

[Steve Conner]

Roughly speaking, every time you mismatch your transformer by a factor of 2 upwards, you lose an octave of bass. So using your 8 ohm transformer into a 32 ohm load, if it went down to 20Hz before, it will crap out at 80Hz.

Not always a bad thing, as the lowest note on the guitar is 82Hz, and the "crapping out" (saturation) generates harmonics that can even give the illusion of more bass.

[Alf]

Thanks Steve, that's just the kind of information I needed !

So it could work for regular guitar. I might try it I just have to check if my two alnicos are 8 or 16 ohm ( celestion blue and gold in one cab )

[Chuck H]

To be frank (and Chuck simultaneously... Using all my bifurcating skills now) if I had a Celestion Blue and a Gold I might build better than using an odd salvaged OT with such limitations to run them. Just sayin'. Of course, if you already use this cab with another amp and can wire the 32 ohm option on a switch it makes a lot more sense.

[Alf]

Of course, if you already use this cab with another amp and can wire the 32 ohm option on a switch it makes a lot more sense.

Yes , I use it with some other amp but the switch option would be very nice.

I just want to try a low power amp which I can turn up without getting too loud. it's just for home
and maybe recording if it sounds good.

[J M Fahey]

Agree with chuck: I would not get into a $200 problem to find use to a $5 part, if you catch my drift.
Since you still have to get a PT , chassis, sockets, tubes, cabinet, plus *everything* else, I would ditch that OT and build a proper amp, instead of one which loses 2 bass octaves and still forces me to use awkward 32 ohm speakers.
jm2c.