Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on June 30, 2023, 11:14:12 pm

Title: JTM45/Bluesbreaker
Post by: TIMBO on June 30, 2023, 11:14:12 pm

Hi guys, This one has been sitting on the shelf for some time now...
It lacked volume mainly due to the PT being a bit under size.
At sometime I changed the PT in the hope to get more output.
From memory it still lack volume and it was promptly sent to shelf to collect dust.
Fast forward to now.....
Circuit checked out good.
The new PT is an unknown and hooked up to some 240v gave me a better idea of it capacity
The taps were labeled but was hard to read
Multiple taps with no 5v
HT is 385-0-385
A couple of 6.3v
OT also an unknown
With 4,8,16ohm sec
After testing it appeared to have approx. 4K primary
Firing up again and my test guitarist still wasn't impressed
Voltages were all good...
Retested the OT and I had the 8ohm load connected to the 8ohm tap so it reflected the 4K primary.
It is now reflecting 8K
Reverb also lacking any real boing, so a few resistor changes has got it in a good place.
Off to the stunt guitarist to give it another bash
(https://i.imgur.com/inuFwTG.jpg)
(https://i.imgur.com/bxRqsRF.jpg)
(https://i.imgur.com/cjw3tup.jpg)
A new cab constructed

Title: Re: JTM45/Bluesbreaker
Post by: TIMBO on July 01, 2023, 11:14:04 pm

Testing went well, reverb is awesome.
Overall volume has increased with the extra reverb boing
The brite channel is a bit quieter than the normal channel, so a bit more investigation needed.

Title: Re: JTM45/Bluesbreaker
Post by: PRR on July 02, 2023, 12:17:20 am

Quote from: TIMBO on July 01, 2023, 11:14:04 pm

The brite channel is a bit quieter than the normal channel, so a bit more investigation needed.

Note the different cathode resistors. Not meant to be identical.

I think if you play well up the neck the brite channel has enough gain to play well. If you expect norm and brite to play "the same", you have to account for the different tone-flavors against what you play; or use the Volume knobs.

Title: Re: JTM45/Bluesbreaker
Post by: TIMBO on July 02, 2023, 01:32:33 am

Thanks PRR
That makes a lot of sense.

Title: Re: JTM45/Bluesbreaker
Post by: tubenit on July 02, 2023, 04:48:21 am

Nice build!  You come up with some really cool stuff. I always follow your threads with interest!


Thanks for sharing!  with respect, Tubenit

Title: Re: JTM45/Bluesbreaker
Post by: TIMBO on July 02, 2023, 05:17:33 am

No worries, thanks T
This is an on going build
PT/OT matchup JTM45 Build (el34world.com) (https://el34world.com/Forum/index.php?topic=21853.0)
When I got the build together, the cab was way too big.
Condensed it down and now a much better size.
Stuck the original cab on ebay and got $250
Need to buy more parts, HOOT :icon_biggrin: