Metropoulos Forum

Well I finished up the 50 Watter today...everything worked properly on first start up. I have one question about the bias setting. As you can see from the PDF below the V4 reading was 36.0 and the V5 reading was 34.0 even with the pot fully counterclockwise...is this a problem (bias slightly cold). I have included a few pics with close ups of the Larmar PPIMV and Zero Loss effects loop. Both work well.

http://www.huronoc.ca/Pin%201.pdf

I will do a proper "first impression and sound clip" reply later but let me say HOLY CRAP is this amp LOUD (my wife hates it already )

I just put a duet of seimens 34's today and my B+ was 450.. and yes my bias pot was maxed to add I had -34 on one tube and -33 on the other mine is maxed also..I almost forgot nice job!

Put a 33K in place of the 47K in the bias circuit and it should have a better range. Every plexi style amp I've built needed a 33K, I just do it right off the bat now.

eddie25 wrote:Put a 33K in place of the 47K in the bias circuit and it should have a better range.

Agree...

I used a 36K.....It was the next-smallest resistor I had laying around. The bias trim pot is now in the middle of its range when setting the bias in the mid 30's.

syscokid wrote:

eddie25 wrote:Put a 33K in place of the 47K in the bias circuit and it should have a better range.

Agree...

I used a 36K.....It was the next-smallest resistor I had laying around. The bias trim pot is now in the middle of its range when setting the bias in the mid 30's.

Thanks for the reply... I thought that may be the solution. Played the amp all weekend...I am really suprised at how nice this amp sounds clean (easy to find the sweet spot where it's clean when played lightly then digs in when you pick harder). I can't imagine this amp without the PPIMV as I have never had a louder amp ( this thing seems twice as loud as the 100W Mesa Roadster I had).

The only problem I have so far is a brutal ground loop when I use my TC G System in the effects loop. It sounds great and very transparent with just a pedal in the loop so just a ground loop problem.. This amp loves pedals in front..especially my BB Preamp....

have one question about the bias setting. As you can see from the PDF below the V4 reading was 36.0 and the V5 reading was 34.0 even with the pot fully counterclockwise...is this a problem (bias slightly cold).

Congrats on finally getting your 50 watter up and running. I had the same issue with cold bias. The kit instructions call for a 150k ohm main bias voltage dropping resistor before the diode. Change this to 220k ohm like shown in the schematic in back of the assembly instructions. You should have a 220k ohm in your resistor kit. It will dial right in afterward.

arledgsc wrote:

have one question about the bias setting. As you can see from the PDF below the V4 reading was 36.0 and the V5 reading was 34.0 even with the pot fully counterclockwise...is this a problem (bias slightly cold).

Congrats on finally getting your 50 watter up and running. I had the same issue with cold bias. The kit instructions call for a 150k ohm main bias voltage dropping resistor before the diode. Change this to 220k ohm like shown in the schematic in back of the assembly instructions. You should have a 220k ohm in your resistor kit. It will dial right in afterward.

Thanks... the 220K worked like a charm

Thanks-I finished my 50 watt build and was only able to get my NOS xf2's to 36.6/35.0 @ 436vac. I wasn't sure if the 47K resistor across the bias pot or the 150K before the diode was the solution.