new 50 build-toobes red plate?

bluze81 · Post by **bluze81** » Sun Jun 03, 2007 10:06 am

4 gigs since thursday and tried out new build 1987 amp, sounded great then I saw both nos mullard el34 red plating, tried to adjust on spot with bias trimmer turned all the way for lower volt and still a bit of redplate ,havent had a chance to use the biasrite meter to see where they are,when I first built it I set bias cold at 34ma with plate volts at 435 and tubes were fine until I tried amp with the band,just wondering if I had bias resistor drift out?

Flames1950 · Post by **Flames1950** » Sun Jun 03, 2007 10:30 am

RF oscillation? Did you flash us final build pics already?

bluze81 · Post by **bluze81** » Sun Jun 03, 2007 11:04 am

no rf occilation, sounded fine, I think I posted a final picture? its under 1987 build picts ,if not I will post a new pict, after this storm leaves my area here, its really heavy rain, bluze

bluze81 · Post by **bluze81** » Sun Jun 03, 2007 11:16 pm

checked all resistors for drift,all good and I rechecked my bias and udjusted ,no redplate when playing thru amp, I monitored the biasrite while playing and I know the bias goes up as you play,it went from set 36,to 45 and hit 50 one time when I hit a note or chord real hard, I guess thats normal? the only problem I can find is a ground hum it gets really loud when I get close to v2 area,so perhaps a bad contact solder joint on the socket, I will try another tube in that spot first, thanks for any help,all comments welcomed. bluze

darrell · Post by **darrell** » Mon Jun 04, 2007 1:25 am

Was the amp pluged in to the same wall socket or where you some where else? The reason I ask is wall voltage one may be 110 and one 125 or higher..
Just a thought man.
Check the wires and solder joint on pin 5 . My slx was red striping a tube and it was the wire on pin 5 had a cold solder joint..
Darrell

bluze81 · Post by **bluze81** » Mon Jun 04, 2007 1:43 am

darrell wrote:Was the amp pluged in to the same wall socket or where you some where else? The reason I ask is wall voltage one may be 110 and one 125 or higher..
Just a thought man.
Check the wires and solder joint on pin 5 . My slx was red striping a tube and it was the wire on pin 5 had a cold solder joint..
Darrell

Thats a thought, It Redplated at our new rehearsal room,I havent had time to check the wall volts ac outlet,its a brand new building, hmmm, thanks Darrell

908ssp · Post by **908ssp** » Mon Jun 04, 2007 10:04 am

I bought 10 NOS EL34 Mullards a while back unmatched. Well unmatched is an understatement. Some ran red some ran ice cold. The tubes themselves had a huge variation. I could run all of them but not without changing the resistor. The resistor being out of spec may not be the issue as the tube while still perfectly usable are.

bluze81 · Post by **bluze81** » Mon Jun 04, 2007 3:04 pm

908ssp wrote:I bought 10 NOS EL34 Mullards a while back unmatched. Well unmatched is an understatement. Some ran red some ran ice cold. The tubes themselves had a huge variation. I could run all of them but not without changing the resistor. The resistor being out of spec may not be the issue as the tube while still perfectly usable are.

Thanks Alex, the tubes are a real good matched set I have used them in another amp with no problems, I think it might be the outlets where we rehearse ,the more I think about it makes more sense, it wont redplate at home or at my shop, just at the rehearsal spot, so I will keep at it and check the wall outlets, the amp sounds wonderfull! real loose but definite,if that makse sense? I love the marstran 139 output transf, with a 3h choke and Metro power transformer ,a real nice combonation of parts, thanks for all the replys,Steve

darrell · Post by **darrell** » Tue Jun 05, 2007 7:18 am

Make shure to check the ground in the soket if its a new building they may have there wires crosed at the wall soket or the ground isnot hooked up/ or poor conennection.
D.

bluze81 · Post by **bluze81** » Tue Jun 05, 2007 6:23 pm

While reading another post It hit me, I didnt ground my speaker jacks! what a dumba## ! so I ran a ground and no more hum when you get close to the speaker jacks or by v2 and amp sounds better, could that have been why the tubes redplated? they arent doing that now and bias is set a bit cool, bluze