JTM45/100 tube trouble

The good, the bad and the ugly.

Moderator: VelvetGeorge

Post Reply
trotter1
New Member
Posts: 2
Joined: Fri Jun 23, 2017 6:24 pm
Just the numbers in order: 13492
Location: Alberta, Canada

JTM45/100 tube trouble

Post by trotter1 » Fri Jun 23, 2017 7:21 pm

I am trying to get my JTM45/100 build finished up and am having bias trouble and tube trouble. I am using GEC KT66's and the problem is. As the amp warms up the bias increases on it own and the tubes in sockets 4 and 5 red plate. Valves 6 and 7 seem to be ok. I used the B. Batz layout and have check my work numerous times. The only mod I made was the bias resister from 56k to 47k and the addition of a 25k bias pot. Any help would be appreciated.

User avatar
neikeel
Senior Member
Posts: 6889
Joined: Tue Dec 06, 2005 8:31 am
Location: Suffolk, England

Re: JTM45/100 tube trouble

Post by neikeel » Tue Jun 27, 2017 11:43 am

Post some clear pictures of your work.

What voltages do you get before you put the GECs in? Output socket please

How are you measuring bias?

Have you tried swapping tubes?

Are your OT primaries wired up correctly?

Have alook at these things and post back and we will get you up and running :clap:
Neil

danman
Senior Member
Posts: 678
Joined: Tue Sep 10, 2013 9:09 pm
Just the numbers in order: 13492

Re: JTM45/100 tube trouble

Post by danman » Tue Jun 27, 2017 8:10 pm

Check everything that neikeel mentioned. Also measure your negative DC bias voltage at pin 5 of the sockets that are redplating. See if you are getting a stable negative voltage or not. You can do this with the power tubes removed. Another possibility is the OT primaries are reversed and the amp is oscillating which will start the redplating to set in.

Roe
Senior Member
Posts: 4972
Joined: Thu Apr 13, 2006 1:36 pm
Just the numbers in order: 7
Location: Drontheim. Norwegen
Contact:

Re: JTM45/100 tube trouble

Post by Roe » Wed Jun 28, 2017 3:07 am

Test with cheaper tubes first. Measure voltage at pins 3 and 4 and check bias
http://www.myspace.com/20bonesband" onclick="window.open(this.href);return false;
http://www.myspace.com/prostitutes" onclick="window.open(this.href);return false;
Super 100 amps: 1202-119 & 1202-84
JTM45 RS OT JTM50 JMP50 1959/2203/34/39

trotter1
New Member
Posts: 2
Joined: Fri Jun 23, 2017 6:24 pm
Just the numbers in order: 13492
Location: Alberta, Canada

Re: JTM45/100 tube trouble

Post by trotter1 » Sun Jul 23, 2017 10:47 pm

Got it figured out, Was some badly soldered connections. Thanks for everybody's help. I was thinking of changing the secondary's on my classic tone 40-18068 to the higher voltage. Any thoughts would be welcome.

Post Reply