More Problems on my 50watt build :(

el34on11 · Post by **el34on11** » Sun Jan 28, 2007 11:29 am

Started testing voltages and doesn't seem right, as well when I plugged in the el34's to set the bias nothing but high pitched squeel and hum(very loud)

All the heater voltages are at 3.3 to 3.4 volts
Plugged in the pre's and they lit up so I threw the standby and here are the voltages I got on the pre's

V1 pin 1 152 -pin 3 .8 -pin6 199.7 -(pin 8 0--?)

V2 pin 1 158 -pin 3 1.0 -pin6 286 -pin7 151 -pin8 160

V3 pin 1 219 -pin 3 39 - pin6 209 -pin 8 39

I know that is not right, but I went ahead and installed the el34's to test again and set bias and BAM----SQUEEL AND HUM! I shut it down right away and rechecked my wiring. Can't figure this out.....

Oh BTW I used the great layout provided by Billy Batz for the 1987, and did add the third 50/50uf filter cap and placed it beside the choke on top of the chassis....

Any ideas where to start looking....I don't have a good camera to get good chassis shots right now but will try to post some later today...
Where did I screw up?

Thanks
D

SDM · Post by **SDM** » Mon Jan 29, 2007 7:57 am

As to the squealing this thread may help:
http://forum.metroamp.com/viewtopic.php ... ght=#95491
You may have other issues though which pics would likely help with, the voltages do not look bad assuming a 450V ish B+(except V1 pin 8, are you sure about that?). Voltages will rise some without the power tubes in and 450V is found in some 50 watt PT's. Also I'm sure you meant pin 6 instead of pin 5 above in the measurements.

Bill Durham · Post by **Bill Durham** » Mon Jan 29, 2007 8:42 am

One thing to try, flip the wires from the OP tranny to the output tubes. If you have those backwards, you are putting positive feedback into the PI instead of negative.

give it a try
BD

el34on11 · Post by **el34on11** » Mon Jan 29, 2007 9:14 am

SDM wrote:As to the squealing this thread may help:
http://forum.metroamp.com/viewtopic.php ... ght=#95491
You may have other issues though which pics would likely help with, the voltages do not look bad assuming a 450V ish B+(except V1 pin 8, are you sure about that?). Voltages will rise some without the power tubes in and 450V is found in some 50 watt PT's. Also I'm sure you meant pin 6 instead of pin 5 above in the measurements.

Thanks SDM

Doh! I did mean pin 6 and fixed it in my post.....

I pulled the board last night and found that I had reversed the two wires from the bias resistors? I think that is what they are called, that go to the output tubes.
Going to put the board back in tonight when I get home and I'm trying to get some pics uploaded
Thanks
D

SDM · Post by **SDM** » Mon Jan 29, 2007 9:21 am

el34on11 wrote: I pulled the board last night and found that I had reversed the two wires from the bias resistors? I think that is what they are called, that go to the output tubes.
D

That has exactly the same effect as reversed OT primaries on the pin 3's of the output tubes (as in the thread I posted and Bill's comments above). So swapping around those wires to the pin 5's that you have reversed should kill that squeal.

el34on11 · Post by **el34on11** » Mon Jan 29, 2007 9:35 am

Bill Durham wrote:One thing to try, flip the wires from the OP tranny to the output tubes. If you have those backwards, you are putting positive feedback into the PI instead of negative.

give it a try
BD

Bill thanks

I did reverse some wires and fixed that,will give it a go when I get the board back in and and fire it back up....
OT hooked up as per the diagram white to V5 red to V4 and broun CT.
Hope that is correct.

If there is still a problem will try lifting the nfb.as per the link in SDM's reply
Thanks Bill
D

Metropoulos Forum

More Problems on my 50watt build :(

More Problems on my 50watt build :(

Squeel and hum

Re: Squeel and hum