Hi, i'm new to the forum, to Dynaco and to tubes.
I have rather a sad story regarding a pristine factory wired st35 which is driving me mad.
I bought the amp on the Swedish equivalent of ebay about 2 years ago and started researching. Didn't do anything for a long time then found a place here on Stockholm to check it out. They said it was in perfect condition, changed the power cord which had been cut and the fuse holder which was broken. It even had the original working dynaco valves and had almost no signs of use.
i didn't have a preamp or appropriate speakers so it stayed on the shelf until I got the speakers.
When I got some speakers i connected it up to a 110v transformer and turned it on. It worked but was very quiet, distorted badly on turning up the source volume and was noticably quieter on one channel.
I decided that i needed to replace the quad filter capacitor though i was very reluctant to do anything at all as i don't want ot die yet and didn't want to touch the factory wiring.
The only source for a replacement quad cap was dynakit. I decided to order a transformer kit and two quad caps so I could build a dynakit st35 in preparation for restoring the dynaco st35.
The parts arrived, never again unfortunately due to high duty here in Seeden, and I set to making a replica chassis. That done I built the dynakit amp and was glowing with satisfaction mostly because I managed but also because of the sound. I followed the original dynakit st35 diy manual, wiring for 220 v. in the process I discovered that the old dynaco amp also had the optional 110/220 power transformer and had been wired for 220. that explained why it had been so quiet! Though not the distortion or the even quieter right channel.
In the mean time I had worked out how to measure voltage using a multimeter and found that there was no reading on pins 3,4 and 5 on the valves on the right channel.
So far, so good, but what follows is a tale of unrelenting failure and bewilderment.
When I put together the dynakit st35 i used a pair of stuffed pcbs I bought on ebay from a guy in Canada. I only had enough nuts and bolts to fasten two each of the four corners of the chassis when i built the amp but, as I said it worked fine, for 4 days! After turning it off (of course) turning it over and putting in the remaining nuts and bolts I turned it on, heard a paph sound and it went dead. The fuse had blown. Checked the wiring found nothing except possibly that the mounting rings for valve sockets 3 and 6 were in contact with the chassis, though they had been before tightening up the pcbs as well. Anyway, fixed that, put in a new fuse and turned on again. No music, just a loud click and humming, mostly from one channel though I didn't leave it on long enough to check carefully if the humming was from one or both channels.
At this point I decide to turn my attention to the old st35.
I put in the other new quad cap checked the wiring and powered it up with exactly the same results!! Loud click and hum.
As I have duplicates for all the components I have tried putting together combinations in order to find where the problem(s) lie. This culminated in yesterdays effort of replacing all the resistors on the Canadian replica pcbs as they were all giving worse readings than the resistors on the original pcbs, replacing the silicon diodes, putting in new valves, checking and double checking the wiring including using the multimeter to check for continuity and finally turning on, first at 110. Dim glow from 12dw7 valves, no noise. Then at 220v, no click, no hum and the valves lit up but no music. I had turned the lights out to check the valves were glowing when, in the dark I saw a spiral of smoke!!! Turn off and sure enough there are burn marks at the square lug of the quad capacitor where the red leads from the output tranformers are soldered on.
If anyone has any suggestions they would be much appreciated.
I don't have the equipment to test the transformers or the capacitors but I think they are the most likely suspects.
Also some of the replacement components that I have tried are not exactly the same as the specs, ie I was using a 47 ohm (not 50) resistor across the square and round lugs and 100ohm (not 95) resistor between the triangle and chassis mounting lug (earth), the silicon diodes were 1amp rather than 500ma. Could any of these have caused the problems? Even if the diodes did cause the last problem they don't explain what was wrong with the new build amp as I recycled the old diodes and the new ones gave similar readings using the multimeter.
The trouble with coming up against a series of setbacks like this is that they take all the fun out of it. Every time I turn on my heart is in my mouth. I'm also concerned for the health of the rest of the components not to mention my own:@.
Hope to rediscover both the fun and the music.
Apparently Dynaco had a distributor in Sweden, possibly in the 60's.
Take care.
Brian
I have rather a sad story regarding a pristine factory wired st35 which is driving me mad.
I bought the amp on the Swedish equivalent of ebay about 2 years ago and started researching. Didn't do anything for a long time then found a place here on Stockholm to check it out. They said it was in perfect condition, changed the power cord which had been cut and the fuse holder which was broken. It even had the original working dynaco valves and had almost no signs of use.
i didn't have a preamp or appropriate speakers so it stayed on the shelf until I got the speakers.
When I got some speakers i connected it up to a 110v transformer and turned it on. It worked but was very quiet, distorted badly on turning up the source volume and was noticably quieter on one channel.
I decided that i needed to replace the quad filter capacitor though i was very reluctant to do anything at all as i don't want ot die yet and didn't want to touch the factory wiring.
The only source for a replacement quad cap was dynakit. I decided to order a transformer kit and two quad caps so I could build a dynakit st35 in preparation for restoring the dynaco st35.
The parts arrived, never again unfortunately due to high duty here in Seeden, and I set to making a replica chassis. That done I built the dynakit amp and was glowing with satisfaction mostly because I managed but also because of the sound. I followed the original dynakit st35 diy manual, wiring for 220 v. in the process I discovered that the old dynaco amp also had the optional 110/220 power transformer and had been wired for 220. that explained why it had been so quiet! Though not the distortion or the even quieter right channel.
In the mean time I had worked out how to measure voltage using a multimeter and found that there was no reading on pins 3,4 and 5 on the valves on the right channel.
So far, so good, but what follows is a tale of unrelenting failure and bewilderment.
When I put together the dynakit st35 i used a pair of stuffed pcbs I bought on ebay from a guy in Canada. I only had enough nuts and bolts to fasten two each of the four corners of the chassis when i built the amp but, as I said it worked fine, for 4 days! After turning it off (of course) turning it over and putting in the remaining nuts and bolts I turned it on, heard a paph sound and it went dead. The fuse had blown. Checked the wiring found nothing except possibly that the mounting rings for valve sockets 3 and 6 were in contact with the chassis, though they had been before tightening up the pcbs as well. Anyway, fixed that, put in a new fuse and turned on again. No music, just a loud click and humming, mostly from one channel though I didn't leave it on long enough to check carefully if the humming was from one or both channels.
At this point I decide to turn my attention to the old st35.
I put in the other new quad cap checked the wiring and powered it up with exactly the same results!! Loud click and hum.
As I have duplicates for all the components I have tried putting together combinations in order to find where the problem(s) lie. This culminated in yesterdays effort of replacing all the resistors on the Canadian replica pcbs as they were all giving worse readings than the resistors on the original pcbs, replacing the silicon diodes, putting in new valves, checking and double checking the wiring including using the multimeter to check for continuity and finally turning on, first at 110. Dim glow from 12dw7 valves, no noise. Then at 220v, no click, no hum and the valves lit up but no music. I had turned the lights out to check the valves were glowing when, in the dark I saw a spiral of smoke!!! Turn off and sure enough there are burn marks at the square lug of the quad capacitor where the red leads from the output tranformers are soldered on.
If anyone has any suggestions they would be much appreciated.
I don't have the equipment to test the transformers or the capacitors but I think they are the most likely suspects.
Also some of the replacement components that I have tried are not exactly the same as the specs, ie I was using a 47 ohm (not 50) resistor across the square and round lugs and 100ohm (not 95) resistor between the triangle and chassis mounting lug (earth), the silicon diodes were 1amp rather than 500ma. Could any of these have caused the problems? Even if the diodes did cause the last problem they don't explain what was wrong with the new build amp as I recycled the old diodes and the new ones gave similar readings using the multimeter.
The trouble with coming up against a series of setbacks like this is that they take all the fun out of it. Every time I turn on my heart is in my mouth. I'm also concerned for the health of the rest of the components not to mention my own:@.
Hope to rediscover both the fun and the music.
Apparently Dynaco had a distributor in Sweden, possibly in the 60's.
Take care.
Brian
.