mijohnThat's good, you have the right transformer. I made that comment because you wrote that the amp was stamped 220V.lagwil wrote:mijohn wrote:Could an overstressed power transformer be causing the problem and producing the mechanical hum, it's rated for 220V and you're giving at least 235V. A Dynakit PA521 transformer rated at 240V would be better for your area.
PA521 is what I have.
/Wilhelm
+3
mijohn
Bob Latino
MechEngVic
7 posters
Very low bias and hum on Dynakit ST-70
mijohn- Posts : 119
Join date : 2013-06-19
lagwil- Posts : 18
Join date : 2019-05-29
peterh wrote:lagwil wrote:mijohn wrote:Could an overstressed power transformer be causing the problem and producing the mechanical hum, it's rated for 220V and you're giving at least 235V. A Dynakit PA521 transformer rated at 240V would be better for your area.
PA521 is what I got.
/Wilhelm
Du kan höra med http://www.lh-musik.se/ för reparation
Peter, är det du som är Mr Tubular Well?
peterh- Posts : 1832
Join date : 2012-12-25
Location : gothenburg, sweden
lagwil wrote:peterh wrote:lagwil wrote:mijohn wrote:Could an overstressed power transformer be causing the problem and producing the mechanical hum, it's rated for 220V and you're giving at least 235V. A Dynakit PA521 transformer rated at 240V would be better for your area.
PA521 is what I got.
/Wilhelm
Du kan höra med http://www.lh-musik.se/ för reparation
Peter, är det du som är Mr Tubular Well?
Yes
lagwil- Posts : 18
Join date : 2019-05-29
@peterh I just ordered a new GZ34 from you!
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Last edited by PeterCapo on Mon Nov 30, 2020 8:13 pm; edited 1 time in total
peterh- Posts : 1832
Join date : 2012-12-25
Location : gothenburg, sweden
Thanks for that. It's in the post together with santa claus million parcels!lagwil wrote:@peterh I just ordered a new GZ34 from you!
Rick Green- Posts : 4
Join date : 2017-01-09
Age : 59
Location : Stuart Florida
Hello , I am curious if you have resolved your hum problem? If so what was it? I suspect it is coming from the main transformer mechanically. It would be nice to see where the amp is located some pictures of what it is sitting on in its normal environment. Can you measure the loudness of the hum or is it just perceptible? Is the hum 50 Hz or 100Hz?
lagwil- Posts : 18
Join date : 2019-05-29
Rick Green wrote:Hello , I am curious if you have resolved your hum problem? If so what was it? I suspect it is coming from the main transformer mechanically. It would be nice to see where the amp is located some pictures of what it is sitting on in its normal environment. Can you measure the loudness of the hum or is it just perceptible? Is the hum 50 Hz or 100Hz?
Hi, no the hum is not solved. I tried two different GZ34 rectifiers and both gives only 0.44 V bias. Something is definitely wrong. I will try to get some professional help to solve it.
lagwil- Posts : 18
Join date : 2019-05-29
At last I found the problem with the help of a professional Dynaco repairman! The new quadcap was broken.
DC92 likes this post
DC92- Posts : 21
Join date : 2015-05-28
So, as usual, Bob Latino's original diagnosis of a bad QuadCap was correct! So did the replacement QuadCap fix the Bias issue, too?
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lagwil- Posts : 18
Join date : 2019-05-29
DC92 wrote:So, as usual, Bob Latino's original diagnosis of a bad QuadCap was correct! So did the replacement QuadCap fix the Bias issue, too?
Yes it did.
/Wilhelm
DC92 likes this post
DC92- Posts : 21
Join date : 2015-05-28
I was curious because I found your post looking for a solution to my low bias set readings, but without the hum. It seems my issue was caused by fading output tubes. Anyway, rock on!
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