J
jjohnson
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AM, why don't you keep it and start building some AC boxes? Since you already have the comp DC market all tied up?
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Power Loss when hot
- Thread starter Lazybones1222
- Start date
BoBBY T, Bluegill,Doctor KeyDown,Hammerhead,
I wish you took "mail order" repairs Nomad.
I have two sets other of NOS tubes. I'll try different tubes and see if that works.
The tubes in the Varmint now are the origional Green Stripe Sylvania finals with a NOS green lettered Sylvania drive.
I also have a set of GE NOS finals and a set of RCA NOS finals, and 1 Lindel NOS driver and another Sylvania Green lettered NOS driver to play with. I'll post if that clears the problem.
If not. Any suggestions who to send it to for RF doctoring?
I have two sets other of NOS tubes. I'll try different tubes and see if that works.
The tubes in the Varmint now are the origional Green Stripe Sylvania finals with a NOS green lettered Sylvania drive.
I also have a set of GE NOS finals and a set of RCA NOS finals, and 1 Lindel NOS driver and another Sylvania Green lettered NOS driver to play with. I'll post if that clears the problem.
If not. Any suggestions who to send it to for RF doctoring?
Thanks Adam, but I have an 'everyday' tester and a spare for backup.
What would really get my attention is an old Hickok "Cardmatic" tester. Hickok Cardmatic
The setup was accomplished by inserting a thick cardboard card into a slot. Holes in the card would line up with switch contacts. This made the setup for a particular tube type automatic. Find the card with the right type number, slide it in. Only had one socket of each size.
A few years back a fella designed and sold a computer interface for this tester. Sold as a package for about $1600, I think. Cheaper if you supplied your own Cardmatic to modify. It used an analog input channel to the computer and would display graphic results like a curve tracer. Couldn't quite justify the cost, though. Every time I stumble across one of these testers at a hamfest, it gets away from me. Nobody to blame for that but myself.
And Lazybones, I gotta ask. You ARE hip to watching where the "Plate" controls on a Varmint show their peaks, right?
I meant that as plural, "Peaks". If you're already hip to trimming the driver and final plate coils when tubes get subbed, that's cool. If not, comparing one tube to the next one can be deceptive when the old tube and the new one have a big difference in their internal capacitance. This can mess with where the "Plate Tune" control for that tube shows a peak. With only one tube driving one more, this won't be a big deal, but if either the driver "Plate" or the final Plate tune control is all the way at one end of its travel, there is no mechanical end-stop to go "clank" and show you where the end-of-travel occurs. Those controls will spin 360 degrees, and if they show only ONE peak in one full turn of the knob, this is trouble. It should show TWO peaks in one full turn of the knob. Doesn't matter if those two peaks are right next to each other, of if they are 180 degrees apart. What counts is that you see TWO of them. If not, you'll find that your "peak" occurred with the plates at one or the other end of ELECTRICAL (not mechanical) travel. If the plates are either all the way apart or fully meshed at your "peak", this means it really WASN'T a peak, just the control going almost far enough.
If subbing a tube moves that peak position on the Plate knob far enough, it will move past the range of the knob, and puts the ACTUAL peak past the range of the knob to reach. This is when it's time to trim the coil for that plate circuit, to bring the control back into range. Until that is done, the tube is running as if you purposely cranked the knob off of the peak position. But only because it wouldn't travel that far.
If either Plate control flunks the "two peaks" test, it's time to fix that problem, before any tubes suffer from it.
Gotta get some pics of the "blown fuse" syndrome. The connection from the cathode pin on the tube to the actual cathode inside is through a thin ribbon of what looks like aluminum, spot-welded to the pin inside the tube. An amplifier that is run out of 'peak' tune will overheat that weak link and pop it. Leaves a tiny ball of metal on each side of a small gap. Looks just like the blown element in a glass fuse, sometimes. Once this happens, that tube is permanently dead. Have to resist telling the customer that all he has to do is reach in there and replace the 'fuse'. Gotta figure they won't laugh.
It's tough to get a good pic of parts inside a tube. Sure would be a cute image, though.
73
What would really get my attention is an old Hickok "Cardmatic" tester. Hickok Cardmatic
The setup was accomplished by inserting a thick cardboard card into a slot. Holes in the card would line up with switch contacts. This made the setup for a particular tube type automatic. Find the card with the right type number, slide it in. Only had one socket of each size.
A few years back a fella designed and sold a computer interface for this tester. Sold as a package for about $1600, I think. Cheaper if you supplied your own Cardmatic to modify. It used an analog input channel to the computer and would display graphic results like a curve tracer. Couldn't quite justify the cost, though. Every time I stumble across one of these testers at a hamfest, it gets away from me. Nobody to blame for that but myself.
And Lazybones, I gotta ask. You ARE hip to watching where the "Plate" controls on a Varmint show their peaks, right?
I meant that as plural, "Peaks". If you're already hip to trimming the driver and final plate coils when tubes get subbed, that's cool. If not, comparing one tube to the next one can be deceptive when the old tube and the new one have a big difference in their internal capacitance. This can mess with where the "Plate Tune" control for that tube shows a peak. With only one tube driving one more, this won't be a big deal, but if either the driver "Plate" or the final Plate tune control is all the way at one end of its travel, there is no mechanical end-stop to go "clank" and show you where the end-of-travel occurs. Those controls will spin 360 degrees, and if they show only ONE peak in one full turn of the knob, this is trouble. It should show TWO peaks in one full turn of the knob. Doesn't matter if those two peaks are right next to each other, of if they are 180 degrees apart. What counts is that you see TWO of them. If not, you'll find that your "peak" occurred with the plates at one or the other end of ELECTRICAL (not mechanical) travel. If the plates are either all the way apart or fully meshed at your "peak", this means it really WASN'T a peak, just the control going almost far enough.
If subbing a tube moves that peak position on the Plate knob far enough, it will move past the range of the knob, and puts the ACTUAL peak past the range of the knob to reach. This is when it's time to trim the coil for that plate circuit, to bring the control back into range. Until that is done, the tube is running as if you purposely cranked the knob off of the peak position. But only because it wouldn't travel that far.
If either Plate control flunks the "two peaks" test, it's time to fix that problem, before any tubes suffer from it.
Gotta get some pics of the "blown fuse" syndrome. The connection from the cathode pin on the tube to the actual cathode inside is through a thin ribbon of what looks like aluminum, spot-welded to the pin inside the tube. An amplifier that is run out of 'peak' tune will overheat that weak link and pop it. Leaves a tiny ball of metal on each side of a small gap. Looks just like the blown element in a glass fuse, sometimes. Once this happens, that tube is permanently dead. Have to resist telling the customer that all he has to do is reach in there and replace the 'fuse'. Gotta figure they won't laugh.
It's tough to get a good pic of parts inside a tube. Sure would be a cute image, though.
73
Lazybones1222 said:
Since Adam hijacked this thread.........
Adam, it's a supply-and-demand world; maybe you could get some "Hamsexy" guy to buy it off of you.
BTW Adam, thanks for the 2 Transistor Amp that you donated to our affair earlier this month, it was won by "Dirty White Boy" out of upstate Ohio.
Sorry that you didn't make it down, you were expected.
.
BTW - the amp does peak twice on both plate controls. It is doing the same thing with the NOS tubes swapped out.
Hmmmmm.....could it be those three Mallory 100MF 350V capacitors getting weak?
Hmmmmm.....could it be those three Mallory 100MF 350V capacitors getting weak?
Yes it could be, sure enough. If they are original, they are on borrowed time. If you replace them, and the problem doesn't go away, getting rid of the old filters was still a good idea. They would not have survived for long, if you put them back into regular service.
73
73
westgateparts.com
Good grief. He has the 100 uf capacitors marked as "pf". That's the part you want. Never mind the "pf" misprint.
350 Volt is hard to find in the original package. The 'axial' package with one lead wire out each end is harder to find. The 450 Volt parts will be easier to locate. They'll work fine. Just don't forget to replace the bleeder resistors at the same time. Cheap insurance. A bad bleeder resistor could slam a new filter cap.
73
Good grief. He has the 100 uf capacitors marked as "pf". That's the part you want. Never mind the "pf" misprint.
350 Volt is hard to find in the original package. The 'axial' package with one lead wire out each end is harder to find. The 450 Volt parts will be easier to locate. They'll work fine. Just don't forget to replace the bleeder resistors at the same time. Cheap insurance. A bad bleeder resistor could slam a new filter cap.
73
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