Blues Jr lives.

[jim]

A couple years I applied Mark Huss's mods to a buddy's Blues Jr and it sounded good---not fantastic and maybe not worth the trouble. Now recently it was blowing heater fuses and I found a burnt trace. While removing the heat baked boards I damaged the brittle ribbon cable connecting the main board to the tube board. Maybe it could be fixed, maybe not.   I decided to install Doug's new Blues Jr Circuit boards because at this point I owned the amp.

I would like to thank Doug for reverse engineering that mess into something understandable, repairable and familiar. I added the MM OT with multiple taps because with
speaker options a small amp is more interesting. (We all tried a "Champ on a Stack" and loved it)  My Blues Jr. fired up right away and worked--never had that happen before.  The only problem is the resonance (Meat) pot which is very scratchy -- and a replacement pot was the same. The effect brings out a subtle low overtone rather than "bassifying" the whole band of tone.  I will replace the pot with a resistor of midway value because I want the effect permanent. 

So my question is this--I want to add a presence pot in its place. Should I just use the Tweed Bassman presence circuit?  If so, Where can I find a 5K control pot?
Jim

[dude]

Right here on Hoffman Amps, go to top of this page and look for pots
 

al

[Fresh_Start]

Yeah, those ribbon cables are problems waiting to happen. My Blues Jr. ate power tubes until I added adjustable bias. Unfortunately, I had to partially remove the main board to get that done.  Sounded nice for a while with cooler bias, but the amp has been infested with gremlins ever since.

Cheers,

Chip

[jim]

Well problems are fixed now for me.  I'll get some parts for the presence control from Doug and run with it.  It has nice tone in a small lightweight package but it was meant to be disposable. $579.00 at Guitar Satan.....Guess we showed 'em.  Jim

[Backwoods Joe]

Installed Doug's tube board, removed the ribbon cables and added an adjustable bias pot on a Blues Junior a while back. Everything about Doug's tube board (actually I ordered tube board kit with sockets and screws and such) worked flawlessly. I was surprised at how much better the amp sounded after it was biased correctly and best of all the amp should last for many years now.

[jim]

The original fixed nonadjustable bias was way hot...headroom was limited and tube life short.  Doug engineered the layout and the fitting of the boards exactly right and I am sure there are plenty of Blues Jr fans that will eventually need this fix.

[EL34]

That's awesome to hear after seeing so many post of guys that were not able to install the BJ Boards correctly
Looks like you did a nice job


I'll add a link to my BJ board post to this post so folks can see a success story

[jim]

Thanks, Doug--needed to hear that. I found that the resonance control adds some gain even if the pot is turned fully counterclockwise.  I loose some clean volume.  I had no luck with a presence control, again it added gain. It make sense because you are tinkering with feedback. I like the meat effect but I might use a push-pull here to unground the effect for a louder clean. Otherwise sounds better that it ever did    .   Jim
 
 

[DummyLoad]

I had no luck with a presence control, again it added gain.

how is that possible? presence ckt. does not add gain. it's just the opposite, it's NFB. yes, gain is relative to wiper position, but if presence ckt. is disconnected, amp gain will increase overall. if not, check OT wiring.

--pete