Metropoulos Forum

Thanks RR! I have pretty much decided that the issue is the Chinese KT66's. I had the same results as you, my GEC's never squeal. Nor do 6L6's put in just to test the theory.

The 5.6k grid resistor fix has worked for everyone, to my knowledge. And the next update to the instructions will add these as standard. With a little explanation.

George

BTW here is the wiki page: http://metroamp.com/wiki/index.php/Outp ... _resistors" onclick="window.open(this.href);return false;

VelvetGeorge wrote:Thanks RR! I have pretty much decided that the issue is the Chinese KT66's. I had the same results as you, my GEC's never squeal. Nor do 6L6's put in just to test the theory.

The 5.6k grid resistor fix has worked for everyone, to my knowledge. And the next update to the instructions will add these as standard. With a little explanation.

George

BTW here is the wiki page: http://metroamp.com/wiki/index.php/Outp ... _resistors" onclick="window.open(this.href);return false;

You bet George!

I put the 5.6k's in there and viola! ... quiet as a mouse in regards to the standby switch. That's a good idea to just include these resistors as "from the get go" items.

I've logged at least 6 hours on this amp today, it sounds FANTASTIC! Everybody should have one of these amps... I gotta get one!

I installed the 5.6k resistors on mine and it worked for a short while. It took away the squeal from the standby switch, but the hotter the amp got, it started to cut out. Then out of nowhere there was no sound until the next day, then I played again the amp got that dirty pot turning static, then it just cut out. I took out the resistors and it worked fine ever since. Is there any modern production KT66's that don't squeal?

Thought I would throw this in...

I just finished my build a few days ago and have had a few intermittent problems including standby switch squeal, so today I go up to try and sort it out with the intention of installing the 5.6 resistor.

I was also having some issues with strange noises and ugly distortion at higher levels so I first changed out V1 with an old RCA 7025 and then a Russian Tung Sol 12AX7. That fixed the problem, so I just went ahead and changed out all the preamp tubes and put in the Tung Sols since I already had them.

Next I thought I would try out a pair of JJ KT66's in place of the Valve Art and that fixed the standby switch problem! So the resistor might have worked but I think the real problem was the tubes.

That being said I put the old VA tubes in my THD Bivalve, which in addition to being a great amp is the perfect tube tester since it requires no biasing. They worked fine in that amp, so it must be something with how the VA interact with the JTM circuit.

Hope this helps someone!

FYI

My amp played fine for almost a year before the squeal started.
It started as a clicking sound (blocking distortion?) that grew louder with time, then eventually it became a squeal.
So apparently as the tubes got older they started to break down. The weird thing is, a new set of Tubes also squealed.
An 820 resistor fixed the problem.

I use VA Kt66 tubes.

5.6K did the trick, added with Zero Loss Effects Loop, fantastic!

I just completed my JTM45, put the KT66 tubes in and flipped the standby on and got the same issue as mentioned here. I need to pick up the 5.6K resistors. I may already have some 1/2W resistors but haven't checked yet. Would those be okay or do I need a different size?

0.5w is more than sufficient. A 100k-470k power resistor across the standby switch also helps with the squeal

Thanks. I didn't really have a squeal. Just the motor boating, although I didn't leave it on very long! If the resistors don't cut it I'll add the power resistor too.

I was able to install the resistors over the weekend and it made no difference at all. I'm going to go through all of the wiring first and if I don't see any issues, I may upload some pictures to see if your eagle eyes can spot anything. I think it may be a grounding issue. I didn't exactly stick to the star grounding scheme so that may be the issue.

Tone_Chaser wrote:I was able to install the resistors over the weekend and it made no difference at all. I'm going to go through all of the wiring first and if I don't see any issues, I may upload some pictures to see if your eagle eyes can spot anything. I think it may be a grounding issue. I didn't exactly stick to the star grounding scheme so that may be the issue.

Are the primaries reversed? (more of an issue on 100w but.............)

I'm using the Classic Tone 40-18033. The Red wires go to the Rectifier tube and the Common and 120V wires go to the Mains fuse Power Switch.

I think I'll open a new thread that shows the build and gets to where I am now. I've started going through the amp and everything looks good so far. I may try the second output jack and see if maybe there is a grounding issue with that one jack.

Tone_Chaser wrote:I'm using the Classic Tone 40-18033. The Red wires go to the Rectifier tube and the Common and 120V wires go to the Mains fuse Power Switch.

I think I'll open a new thread that shows the build and gets to where I am now. I've started going through the amp and everything looks good so far. I may try the second output jack and see if maybe there is a grounding issue with that one jack.

I meant on the OT...........................