Shortness of breath. Badda-boom.
Lower transconductance and gain, higher plate resistance and noise, wandering off operating points, lower power (output tubes), drawing grid current, glowing red hot where it never glowed red hot before, and the ever-popular dark heater. Pick any of the above, they all happen.
Lower transconductance and gain, higher plate resistance and noise, wandering off operating points, lower power (output tubes), drawing grid current, glowing red hot where it never glowed red hot before, and the ever-popular dark heater. Pick any of the above, they all happen.
In class A UL p-p the symptoms with high gm tubes (6550/KT88 series) usually end up destructive with a red hot anode, screen resistors destruct and usually meltdowns the cathode resistor (if fitted). A fuse in the Bmax line is essential.
With 5U4 directly heated rectifiers, thermal gradients caused by repeated switching on/off over time gradually flakes off the filament coating-> leading to loss of emission.
richj
With 5U4 directly heated rectifiers, thermal gradients caused by repeated switching on/off over time gradually flakes off the filament coating-> leading to loss of emission.
richj
I just got a Radio Craftsmen RC-2 mono amp off of Ebay, and I have an old Sylvania Type 620 tube tester.
The amp lights up, but doesn't pass any audio, just as the seller said.
It uses a push-pull 2 x 6V6GTA output with a 5Y3GT rectifier, and 1 each of a 6J5 metal tube, and a 6SN7GT for the pre-amp stages.
The parts under the chassis seem very simple, in fact less than 18 caps & resistors total, not including the metal can caps (one with 2 elements, one with 3, both Mallory). On one web forum site one guy said he is running his with the original caps, but I'm ordering new ones just in case.
I couldn't find any free schematics for this, so I had to order one for $5, it will take a few days or so.
All the tubes test good in all areas, but both 6V6's test very low on transconductance, it's in the "red" on my tube tester, though all the others were fine. The only major mod I noticed was an aftermarket unversal output xmfr, but it seems ok, no shorts or anything.
One of its leads goes back to pin 7 of the 6J5 (one side of the heater), since I don't have the schematic yet this sounds weird.
There are no controls, just an RCA input jack, and speaker screws for 4,8, & 16 ohms, and no switch, just plug it in to start it.
Do you think the 6V6's are probably shot, even if the caps are ok, and that this alone would cause no sound?
I'm ordering new tubes and will replace all the caps before trying it again.
One weird thing is that there seems to be 2 power resistors with markings new to me, one says RW-4-301K but tests at 300 ohms,
the other says RW-7-222K but tests at 22k ohms, I can't see the logic behind this. Also I should probably replace all the resistors, since I have nearly 100 1/2 watt ones, and some of the originals seem to have drifted more than 20 percent.
---------
My other question, does anyone have a great link to a DIY project or schematic or brand/name/model of any great amp using 2 6V6's in push-pull, with some audio control pots, etc for a real guitar amp.
I'm seeing at lot of circuits on places like Duncan's & MachMat, etc, but what's someone's real fave for sound simplicity, etc. (Maybe I should make a new thread for this last question, unless someone can point me to a great thread on this).
Don't need quite to power of 6L6's.
The amp lights up, but doesn't pass any audio, just as the seller said.
It uses a push-pull 2 x 6V6GTA output with a 5Y3GT rectifier, and 1 each of a 6J5 metal tube, and a 6SN7GT for the pre-amp stages.
The parts under the chassis seem very simple, in fact less than 18 caps & resistors total, not including the metal can caps (one with 2 elements, one with 3, both Mallory). On one web forum site one guy said he is running his with the original caps, but I'm ordering new ones just in case.
I couldn't find any free schematics for this, so I had to order one for $5, it will take a few days or so.
All the tubes test good in all areas, but both 6V6's test very low on transconductance, it's in the "red" on my tube tester, though all the others were fine. The only major mod I noticed was an aftermarket unversal output xmfr, but it seems ok, no shorts or anything.
One of its leads goes back to pin 7 of the 6J5 (one side of the heater), since I don't have the schematic yet this sounds weird.
There are no controls, just an RCA input jack, and speaker screws for 4,8, & 16 ohms, and no switch, just plug it in to start it.
Do you think the 6V6's are probably shot, even if the caps are ok, and that this alone would cause no sound?
I'm ordering new tubes and will replace all the caps before trying it again.
One weird thing is that there seems to be 2 power resistors with markings new to me, one says RW-4-301K but tests at 300 ohms,
the other says RW-7-222K but tests at 22k ohms, I can't see the logic behind this. Also I should probably replace all the resistors, since I have nearly 100 1/2 watt ones, and some of the originals seem to have drifted more than 20 percent.
---------
My other question, does anyone have a great link to a DIY project or schematic or brand/name/model of any great amp using 2 6V6's in push-pull, with some audio control pots, etc for a real guitar amp.
I'm seeing at lot of circuits on places like Duncan's & MachMat, etc, but what's someone's real fave for sound simplicity, etc. (Maybe I should make a new thread for this last question, unless someone can point me to a great thread on this).
Don't need quite to power of 6L6's.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.