Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 72Blazer on June 25, 2021, 03:05:08 pm

Title: New 18 Watt TMB Build (Mojotone Kit)
Post by: 72Blazer on June 25, 2021, 03:05:08 pm

I just completed this build with all new components.  Sounds really good and really quiet with the exception of two very scratchy pots on the master volume channel (Gain and Treble Pots).  I' cleaned both pots to no avail.  Amp tech stated "It is very unusual to have 2 bad CTS pots.  Because these are on the same channel I bet you have a leaky cap somewhere allowing DC to pass.  This would explain why you can't get rid of the scratchiness with cleaner."
Anybody ever run into this type of issue?

Title: Re: New 18 Watt TMB Build (Mojotone Kit)
Post by: 72Blazer on June 25, 2021, 03:05:49 pm

Pic 1

Title: Re: New 18 Watt TMB Build (Mojotone Kit)
Post by: 72Blazer on June 25, 2021, 03:06:19 pm

Pic 2

Title: Re: New 18 Watt TMB Build (Mojotone Kit)
Post by: 72Blazer on June 25, 2021, 03:06:47 pm

Pic 3

Title: Re: New 18 Watt TMB Build (Mojotone Kit)
Post by: sluckey on June 25, 2021, 03:20:36 pm

Quote from: 72Blazer on June 25, 2021, 03:05:08 pm

Anybody ever run into this type of issue?

Yes, we all have. Very common. Most likely the 500pf treble cap. If not that one then one of the .022s.

Title: Re: New 18 Watt TMB Build (Mojotone Kit)
Post by: 72Blazer on June 25, 2021, 04:01:54 pm

It was the 500pf treble cap!
Thanks

Title: Re: New 18 Watt TMB Build (Mojotone Kit)
Post by: 72Blazer on June 25, 2021, 04:47:03 pm

Well it sounded great for about 5 minutes now I got an electrical storm in the MV channel which I did not have before. I've only got one more 500pf cap left in my supply.  I'll try that one and if that don't work I'll start changing out those .022s

Title: Re: New 18 Watt TMB Build (Mojotone Kit)
Post by: 72Blazer on June 25, 2021, 07:20:50 pm

I guess the third time (cap) is a charm...

Title: Re: New 18 Watt TMB Build (Mojotone Kit)
Post by: Willabe on June 25, 2021, 09:13:55 pm

You have to be very careful with those silver mica caps, too much heat soldering them and their toast. 

Title: Re: New 18 Watt TMB Build (Mojotone Kit)
Post by: 72Blazer on June 27, 2021, 12:27:43 pm

Thanks for the tip-I'll use a heat shrink from now on.  Amp still working great but I sure miss fender spring reverb
Has anyone taken a similar amp and and added reverb?

Title: Re: New 18 Watt TMB Build (Mojotone Kit)
Post by: sluckey on June 27, 2021, 12:44:08 pm

That's a good question for 18watt.com.

Title: Re: New 18 Watt TMB Build (Mojotone Kit)
Post by: dude on June 27, 2021, 05:15:15 pm

Yes, several guys at 18 watt added reverb but that was several years ago. Maybe go over there and check it out

Title: Re: New 18 Watt TMB Build (Mojotone Kit)
Post by: Bieworm on June 28, 2021, 03:06:45 am

JMPGuitars designed an amp called " tremolo TMB reverb ". I have built 4 of them already and IMHO it's the best amp I ever heard. I know that's subjective, but nevertheless you're welcome to check it out on 18watt.com. you're very welcome!!!
Not trying  to steal you from EL34world or anything. Great guys here en great Help too...

Title: Re: New 18 Watt TMB Build (Mojotone Kit)
Post by: JB on June 28, 2021, 04:03:43 am

Marshall did make a version of the 18W amp with reverb, the "Master Reverb".  Very rare beast, I had a chance to play one and look inside.  They used a single ECC83 with the send half tapped off the first stage anode and the recovery stage feeding into the second half of the LTPI.  3 x ECC83 in total, single channel with tremolo.