Ralph,
I'm afraid I'm not around for much of the weekend.
I think the transformer pin swap will not make any difference at this stage.
Unless anyone else posts a better suggestion, I recommend:
Set your preamp for a 1 volt AC output when playing 400Hz.
Make sure the same voltage appears on the grid of V4.
Measure the AC voltage across A & B of the interstage transformer. It will be in the order of the mu value of V4.
Now play the 50Hz track and do the same measurements.
The meter readings should be roughly the same.
Also check that the same voltage occurs on pins C & D of the interstage transformer. Then that it occurs between the grid of V3 and ground.
Likewise, the voltage across the primary of the output transformer should aproximate to the grid AC voltage * mu of the output valve - see spec sheet.
Caution: Drop the input level to 0.1volt AC for this test, and calculate accordingly.
Be aware thse are hogh voltage areas. Keep 1 hand behind you when measuring.
Good luck.
I'm afraid I'm not around for much of the weekend.
I think the transformer pin swap will not make any difference at this stage.
Unless anyone else posts a better suggestion, I recommend:
Set your preamp for a 1 volt AC output when playing 400Hz.
Make sure the same voltage appears on the grid of V4.
Measure the AC voltage across A & B of the interstage transformer. It will be in the order of the mu value of V4.
Now play the 50Hz track and do the same measurements.
The meter readings should be roughly the same.
Also check that the same voltage occurs on pins C & D of the interstage transformer. Then that it occurs between the grid of V3 and ground.
Likewise, the voltage across the primary of the output transformer should aproximate to the grid AC voltage * mu of the output valve - see spec sheet.
Caution: Drop the input level to 0.1volt AC for this test, and calculate accordingly.
Be aware thse are hogh voltage areas. Keep 1 hand behind you when measuring.
Good luck.
Hi John,
Measures done 5 mins after switch on:
I set my preamp to output 0,49V because any louder would damage my ears
- Between V4 grid and ground: 0,48V
- AC voltage across A & B of the interstage transformer: 6,74V. Mu of 5687 is specified somewhere in the 16 - 17 range, so I would have expected 7,92V.
- Voltage on pins C & D of the interstage transformer: 6,58V.
- Voltage between the grid of V3 and ground: 6,26V.
So I would expect 6,26V x 3,7 (mu of 300bXLS) = 23,3V. I measured 16,6V.
Ralph
Measures done 5 mins after switch on:
I set my preamp to output 0,49V because any louder would damage my ears
- Between V4 grid and ground: 0,48V
- AC voltage across A & B of the interstage transformer: 6,74V. Mu of 5687 is specified somewhere in the 16 - 17 range, so I would have expected 7,92V.
- Voltage on pins C & D of the interstage transformer: 6,58V.
- Voltage between the grid of V3 and ground: 6,26V.
So I would expect 6,26V x 3,7 (mu of 300bXLS) = 23,3V. I measured 16,6V.
Ralph
YES YES YES YES YES YESYES YES YES YES YES YESYES YES YES YES YES YESYES YES YES YES YES YES!!!
I swapped the bias and grid of the interstage, and there came my treble.
Well John, thank you very much! Now I can start tweaking and trying to get the B+ voltage down etc. Will definitly keep you posted for results!!
Ralph
I swapped the bias and grid of the interstage, and there came my treble.
Well John, thank you very much! Now I can start tweaking and trying to get the B+ voltage down etc. Will definitly keep you posted for results!!
Ralph
Good stuff Ralph.
Remember that the most effective way of lowering the +B will be by reducing or removing that 2uF cap after the rectifier, but it might make the choke buzz.
Also, did you ever measure what was coming out of the transformer? If it's much higher than expected, at the specfied load, maybe wou should contact Wil. If it's his mistake, I'm sure he'd want to correct it.
Cheers,
Remember that the most effective way of lowering the +B will be by reducing or removing that 2uF cap after the rectifier, but it might make the choke buzz.
Also, did you ever measure what was coming out of the transformer? If it's much higher than expected, at the specfied load, maybe wou should contact Wil. If it's his mistake, I'm sure he'd want to correct it.
Cheers,
Ralph,
Before complaining, please post:
The measured primary voltage.
The measured secondary voltage.
The measured secondary current. (Post the DC current if you can't measure AC, we'll calculate).
Please measure all the above in the same time interval ~10min.
The measured secondary DC resistance.
and,
What you specified on your order.
Cheers,
Before complaining, please post:
The measured primary voltage.
The measured secondary voltage.
The measured secondary current. (Post the DC current if you can't measure AC, we'll calculate).
Please measure all the above in the same time interval ~10min.
The measured secondary DC resistance.
and,
What you specified on your order.
Cheers,
Hmm, seems like I've lost one speakers' tweeter 
Swapping the ls-cable made no difference. Hmm, have'nt used those speakers in a long time, so it could have been broken already. Now I'm just a little caucious to attach my normal speakers. But at least I'm glad it's no broken OPT or interstage or tube
Swapping the ls-cable made no difference. Hmm, have'nt used those speakers in a long time, so it could have been broken already. Now I'm just a little caucious to attach my normal speakers. But at least I'm glad it's no broken OPT or interstage or tube
Tweeters can be damaged by HF oscillation. This can be ultrasonic.
It's very unlikely to happen with your circuit, but to be safe you could try to measure if there is any coming out of your speaker connectors.
This will be difficult for you, as you have already stated that your meter's AC frequency range is not good.
Normally you would attach an oscilloscope. Can you borrow one?
If not, I'll post a rectifier circuit, so you can use the DC range of your meter. You'll only need one diode and one capacitor. Perhaps you can imagine how to wire it, just from my description.
It's very unlikely to happen with your circuit, but to be safe you could try to measure if there is any coming out of your speaker connectors.
This will be difficult for you, as you have already stated that your meter's AC frequency range is not good.
Normally you would attach an oscilloscope. Can you borrow one?
If not, I'll post a rectifier circuit, so you can use the DC range of your meter. You'll only need one diode and one capacitor. Perhaps you can imagine how to wire it, just from my description.
Ralph,
No, there will never be DC on your speaker terminals with this design. What I was saying, was that there just might be high frequency AC; too high for you to hear. It's unlikely, but if you want to check, or if you want to measure your frequency response:
You can measure AC with your meter, on the DC ranges, if you put a diode (IN4148, 1N4001, or similar in series with one lead, and add a capacitor (100n or similar) across the meter terminals.
This will measure "peak" rather than RMS value. For a sinewave the conversion factor is: RMS = Peak*0.707.
Cheers,
No, there will never be DC on your speaker terminals with this design. What I was saying, was that there just might be high frequency AC; too high for you to hear. It's unlikely, but if you want to check, or if you want to measure your frequency response:
You can measure AC with your meter, on the DC ranges, if you put a diode (IN4148, 1N4001, or similar in series with one lead, and add a capacitor (100n or similar) across the meter terminals.
This will measure "peak" rather than RMS value. For a sinewave the conversion factor is: RMS = Peak*0.707.
Cheers,
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