Help IDing which tube(s) this OT will work with?

General discussion area for tube amps.

Moderators: pompeiisneaks, Colossal

Post Reply
User avatar
Noel Grassy
Posts: 426
Joined: Thu Feb 09, 2006 5:29 am
Location: Vacuum Tube Valley-Cali

Help IDing which tube(s) this OT will work with?

Post by Noel Grassy »

Howdy, I have a Thordarson xfmr (#24S06) with;

Pri: 4K~14K Ohms CT @ 40 mADC.

Sec: .1~50 Ohms @ 8 watts.

These figures are certainly alot broader than the typical tranny specs I'm more accustomed to seeing!
If a member here can point me in the direction of what I should be looking for in my tube data books I'd be thrilled and thankful.

I'm hoping it might be usable with a common power tube. But I'm prepared to use an uncommon tube(s) as I've got a $hitload of esoteric tubes from various TV & HiFi repair shops that liquidated their stocks.
[Not applicable but, I found four RCA 2A3's in one box!]
All excellent things are as difficult as they are rare__B Spinoza
User avatar
jjman
Posts: 753
Joined: Sat Oct 06, 2007 2:33 pm
Location: Central NJ USA

Re: Help IDing which tube(s) this OT will work with?

Post by jjman »

40 ma is pretty low for 2 PP OP tubes. At least common ones.
If it says "Vintage" on it, -it isn't.
User avatar
Phil_S
Posts: 6048
Joined: Tue Oct 23, 2007 10:12 pm
Location: Baltimore, MD

Re: Help IDing which tube(s) this OT will work with?

Post by Phil_S »

It's potentially more like 10 or 11 watts, but you can control this with plate voltage and bias. Try a pair of 12AU7 or 6SN7 in push pull. A pair means there are two sections in each bottle, so this is more like a 4 tube amp. The typical primary R for a single 12AU7 or 6SN7 (or even 12SN&) is 22K to 27K. Using two of these tubes should cut the primary load in half, making 11K to 14K probably about right. Your 40ma rating is probably OK with these tubes if you keep plate voltage in the appropriate range.
Post Reply