50 watt Help! (sorry a little long)

toner · Post by **toner** » Sun Dec 09, 2007 11:41 pm

Quickdraw wrote:...with the guitar volume just perceptiple all was good... I started picking with a little more pressure and... Ouch! The squeal is still there...

Someone recently had a very similar problem but I can't find that thread or remember what the issue was. I think it may have been a bad filter cap. ?

Hopefully, someone who has experienced this will speak up.

Flames1950 · Post by **Flames1950** » Sun Dec 09, 2007 11:58 pm

I would e-mail about the board, that looks like the holes were slightly too small and the turrets forced in anyways.
That edge is just the way the edge of the sheet is when it comes -- the smoother, squarer edges are the edges cut by the circular saw trimming the boards to size.

Quickdraw · Post by **Quickdraw** » Mon Dec 10, 2007 1:28 pm

Thanks for jumping in Flames,
That makes good sense about the edge of the board, that is exactly what it looks like. Now as much as I want to solve this squealing issue, I'm not sure how much effort it will be worth if I may have to replace that board (except to help hone my troubleshooting skills!). Look at the second pic I posted and you can see the crack on the far upper left turret also.
So, has anyone else seen this before?

Tom

Quickdraw · Post by **Quickdraw** » Mon Dec 10, 2007 9:14 pm

Here is another noggin' scratcher... probably wasn't the greatest idea to run my guitar through the amp last night... but since I was able to pass a small signal through without setting off the screach, I decided to continue and attempt to set the bias (ya I know doesnt fix my problem... but I sure dont want to damage the tubes either). Well to make a long story short (I'm not to good at that either) I went to take my readings at pin 1 and there is 0 voltage WTF? Could I have stumbled on my problem? All my other readings on V4 and V5 were present (but high... pin 3-463, pin4-462, pin5-neg 44, pin 6-461) man this aint right... also all my tube socket htrs are only 2.99

toner · Post by **toner** » Mon Dec 10, 2007 9:27 pm

Maximum negative bias voltage (like the instructions say to start with) won't hurt the tubes and shouldn't cause your noise problem.

How did you have your meter set?

You have to set the meter to a very low mV setting like 200mV or less to set the bias via the 1 ohm resistor. It may only read 0VDC at higher meter settings.

The low AC reading for heaters is very common, especially with cheaper meters.

Sorry if you already knew this. Just trying to help.

Quickdraw · Post by **Quickdraw** » Mon Dec 10, 2007 10:14 pm

nope, all good info toner and sure appreciate it. The meter I was using is a Fluke 114, not top of the line but far from cheap... had it set on mv dc and tried it on auto. Followed the directions to a T. Power on, standby on, Volumes at 0, all the tones and presence were still on 5, and no squealing present... meter on mV, reading at pin 1 v4 and v5... 0.

This has become a real mind blower... I would really like to figure out what I hosed up... but, on a lighter note, George is hookin me up to correct my other board issue... But Im not giving up on this problem yet..\

Billy Batz · Post by **Billy Batz** » Mon Dec 10, 2007 10:24 pm

toner · Post by **toner** » Mon Dec 10, 2007 10:26 pm

It's a 50w Dan.

Billy Batz · Post by **Billy Batz** » Mon Dec 10, 2007 10:26 pm

He has em in the pics anyway. Jeezus I read this thread didnt I. Thats what I get for trying to read threads and jam at the same time.

Billy Batz · Post by **Billy Batz** » Mon Dec 10, 2007 10:46 pm

Quickdraw wrote:nope, all good info toner and sure appreciate it. The meter I was using is a Fluke 114, not top of the line but far from cheap... had it set on mv dc and tried it on auto. Followed the directions to a T. Power on, standby on, Volumes at 0, all the tones and presence were still on 5, and no squealing present... meter on mV, reading at pin 1 v4 and v5... 0.

This has become a real mind blower... I would really like to figure out what I hosed up... but, on a lighter note, George is hookin me up to correct my other board issue... But Im not giving up on this problem yet..\

Maybe a dumb question but did you try turning the bias pot? At max negative voltage you may read 0mV. When you turn up the pot you start getting higher negative readings.

Quickdraw · Post by **Quickdraw** » Mon Dec 10, 2007 10:47 pm

Billy thanks for contributing, I do have 5.6k's on pin 5, but I havent tried shielding the chassis or mounting it in the head case, but I am just about up for anything at this point....

Wow, my bias issue may be that simple? I started at full clock wise as instructed, then when I took the 0 volt reading I attempted to turn it... and again triggered off that incredibly LOUD Squeal... Im going to go turn the bias pot a little, power up and try again...

Blast · Post by **Blast** » Mon Dec 10, 2007 10:52 pm

Quickdraw wrote: also all my tube socket htrs are only 2.99

Heater voltage is AC. Did you measure each heater pin to ground with meter set to AC? Then it's OK. Measure BETWEEN pins 2 & 7 on V4 or V5 to get 6v.

Billy Batz · Post by **Billy Batz** » Mon Dec 10, 2007 10:57 pm

Quickdraw wrote:Billy thanks for contributing, I do have 5.6k's on pin 5, but I havent tried shielding the chassis or mounting it in the head case, but I am just about up for anything at this point....

Wow, my bias issue may be that simple? I started at full clock wise as instructed, then when I took the 0 volt reading I attempted to turn it... and again triggered off that incredibly LOUD Squeal... Im going to go turn the bias pot a little, power up and try again...

you dont have to be super paranoiud about damaging things but you may want to keep feeling the OT to make sure it doesnt get really hot and check the tubes to make sure they dont redplate. Obviously this is where a load box comes in handy.

Quickdraw · Post by **Quickdraw** » Mon Dec 10, 2007 11:23 pm

Ok another update and hopefully another piece of the puzzle. I tried the process I detailed in the message to Billy Batz and found something interesting. With the bias pot fully clockwise it was indeed 0 volts. I couldnt turn the pot without blaring. Hit the Standby tweaked the bias pot a bit... 2.3mv, repeat... 3.4mv, repeat 4.2 and thats as high as i could get it without the blast from the speakers being constant, which now sounds closer to an incredibly loud horn vice squeal... when I secured it I turned off the stanby ... then the power and it squealed while the power drained in a decreasing strobe, and there was what sounded like a light knock simultaneous with the power down strobing sound (eminating from one of the filters or a power tube, I couldnt tell). Output of F1 was a fairly stable but high 464...

toner · Post by **toner** » Mon Dec 10, 2007 11:28 pm

Weird! I think you have a bad power tube.

Just a guess.

Do you have any others to try?