Hi,
+B at 270V suggests to me that the valves are not drawing enough current.
What is the cathode voltage to ground and the grid voltage?
Ciao T
+B at 270V suggests to me that the valves are not drawing enough current.
What is the cathode voltage to ground and the grid voltage?
Ciao T
OK, firstly do not forget that the mains voltage is close to 250V (246V to be exact). Therefore the output voltages are a bit higher than specified in the manual. For example the bias DC is -110V instead of -74V. I do not know if that makes any difference or not.
Measured grid to GND is around -9V. For the cathode ; pin 1 to GND is 2V; pin 4 to GND is 0.48. Heater supply is stable at 2.500V. For this ; plate to GND is 128V and reasonably stable. This is all with 45 valves.
I also noticed that it takes at least 30 minutes for plate voltages to stabilize and the bias is not the same as I left it - I do not know any more - I think I am getting a bit paranoid.
Measured grid to GND is around -9V. For the cathode ; pin 1 to GND is 2V; pin 4 to GND is 0.48. Heater supply is stable at 2.500V. For this ; plate to GND is 128V and reasonably stable. This is all with 45 valves.
I also noticed that it takes at least 30 minutes for plate voltages to stabilize and the bias is not the same as I left it - I do not know any more - I think I am getting a bit paranoid.
Decky, I wish you all the best in sorting out the preamp.
All the recent discussions made me finally get around to putting 45s back into my Tram II. As expected I needed to reset the heater volts but what I've not found before is that I had to reset one CCS which was showing 100V. I swapped the tubes around but they weren't to blame. I had recently noticed that one channel was a little noisy (rustling sounds). It was this channel that needed resetting, I expect a component has drifted, maybe the CCS variable resistor, it is very sensitive to adjustment in the first place. Anyway, I mention this as it's probably worth checking voltages every few months just in case of drift, heat from 2A3s could be a contributory factor.
All the recent discussions made me finally get around to putting 45s back into my Tram II. As expected I needed to reset the heater volts but what I've not found before is that I had to reset one CCS which was showing 100V. I swapped the tubes around but they weren't to blame. I had recently noticed that one channel was a little noisy (rustling sounds). It was this channel that needed resetting, I expect a component has drifted, maybe the CCS variable resistor, it is very sensitive to adjustment in the first place. Anyway, I mention this as it's probably worth checking voltages every few months just in case of drift, heat from 2A3s could be a contributory factor.
Thanks. In my case one pot is very sensitive and the other very lazy. The trouble is when I am close to around 100V if I adjust one the other one is changing - it is very hard to balanced them. I though before that it is CCS to blame - but they are brand new now.
Both of mine are VERY sensitive and I have zero interaction between channels so what you have seems strange.
Hi,
There still seems to be something really wrong.
Can I suggest that you do some more trouble shooting.
It isolate issues I would suggest you temporarily replace the CCS with 560 Ohm / 5W. This creates a simple SRPP and the +B should settle at around 200V and you should see 0.38V across the two 12 Ohm resistors to ground at the DHT's.
This way you can be sure that the whole biasing circuit and the power supplies work 100%.
I would suggest to then test the CCS's by themselves (you can use a 9V Battery) and to set them, together with the parallel resistor to 31.6mA outside the Tram 2.
Then you can put everything back together.
The circuit is really quite simple, it should be pretty easy to find what the problems are.
Ciao T
There still seems to be something really wrong.
Can I suggest that you do some more trouble shooting.
It isolate issues I would suggest you temporarily replace the CCS with 560 Ohm / 5W. This creates a simple SRPP and the +B should settle at around 200V and you should see 0.38V across the two 12 Ohm resistors to ground at the DHT's.
This way you can be sure that the whole biasing circuit and the power supplies work 100%.
I would suggest to then test the CCS's by themselves (you can use a 9V Battery) and to set them, together with the parallel resistor to 31.6mA outside the Tram 2.
Then you can put everything back together.
The circuit is really quite simple, it should be pretty easy to find what the problems are.
Ciao T
Hi,
Yes, whole PCB.
Just a thought, the CCS & PCB require a modification, as the CCS chip requires a "gate stopper", if diyhfs send you new chips and PCB's you may be missing this mod?
Ciao T
Yes, whole PCB.
Just a thought, the CCS & PCB require a modification, as the CCS chip requires a "gate stopper", if diyhfs send you new chips and PCB's you may be missing this mod?
Ciao T
Also just to clarify, I should put 560R between the +B and the anode and leave the output not connected?
Can you just explain in more details how to set the CCS by themselves?
I do not know about that mod - I am reading the assembly manual R1.34 and the CCs PCB looks the same as the one I have (I have not checked all the resistor values). What is the gate stopper? You mean that cut track under the 5.1K resistor?
Can you just explain in more details how to set the CCS by themselves?
I do not know about that mod - I am reading the assembly manual R1.34 and the CCs PCB looks the same as the one I have (I have not checked all the resistor values). What is the gate stopper? You mean that cut track under the 5.1K resistor?
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Hi,
No, I wrote: "replace the CCS with a 560R resistor", it does not say "connect 560 Ohm between +B and anode"
Connect Battery, Multimeter set to current and CCS in series, adjust ccs till multimeter reads 31.6mA.
Ciao T
No, I wrote: "replace the CCS with a 560R resistor", it does not say "connect 560 Ohm between +B and anode"
Connect Battery, Multimeter set to current and CCS in series, adjust ccs till multimeter reads 31.6mA.
Ciao T
...and it sings again. Thanks beardman ! Due to my lack of experience with valves I could not imagine that difference between 2.48V and 2.53V can make such a huge difference for the heater performance. I know better now.
I will monitor the situation and report but at the moment sounds amazing again.
I will monitor the situation and report but at the moment sounds amazing again.
Hi,
Okay, I think these voltages sound ok. Have you tested the wiring around the new output capacitors for shorts to ground?
Ciao T
Okay, I think these voltages sound ok. Have you tested the wiring around the new output capacitors for shorts to ground?
Ciao T
Hi,
Hmmm, I do find that surprising, I did not notice such a sensitivity myself...
Ciao T
Hmmm, I do find that surprising, I did not notice such a sensitivity myself...
Ciao T
I found something similar, when the reg drops out it seemed to operate very erratically or not at all, so I had to take care in fine tuning the resistors feeding the regs.
Anyone using laptop cooling pads? USB LAPTOP NOTEBOOK COOLER COOLING PAD 1 FAN BLUE LIGHT | eBay UK
Anyone using laptop cooling pads? USB LAPTOP NOTEBOOK COOLER COOLING PAD 1 FAN BLUE LIGHT | eBay UK
Notebook cooling pad is a great idea. With 45 valves the heat is not a big issue but every little bit of thermal control helps I guess. Heater regulator (extended) heatsinks are at ~57C after couple of hours of operation.
I am about to assemble another Tram for a friend and I will try to optimize it for 2A3 valves.
I am about to assemble another Tram for a friend and I will try to optimize it for 2A3 valves.
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