Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Paramount => Topic started by: Gerry E. on August 18, 2018, 05:58:11 AM
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Hi:
I have early Paramounts with the v1.1 soft start upgrade kit installed. Is there a simple way to make sure that the voltages to the 300B tubes are in the ballpark? Preferably from the top without the 300Bs installed? I have a meter and know the safety rules from the manuals. Thanks!
Gerry
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From the top, not so much. Performing the voltage checks on the 4 pin socket will give you some data on how the 300B is operating, though it will look really solid until it's almost completely dead.
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Gerry,
Flip the top plate over and elevate the base on something. I use books at the corner. Put the grounding plug in and measure away, safely. I do this from time to time.
Aaron
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Thanks PB and Aaron! Your replies were the little push I needed to do it the right way. I measured one of the amps yesterday and the results were very close to the manual numbers (manual / my results):
A1 74.1V 74.3V
A2 428V 427V
A3 0* 14mV
A4 69.2 69.3V
* Close to zero
I'll measure the 2nd amp in the next day or two.
Gerry
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I was an early Elrog user and had one of the tubes die on me. It took out the cathode resistor along with it. Now, PB reminded me that my choice of cathode resistors was questionable and it most likely was the other way around. They sounded great up until then. Periodic testing is easy to do and gives you the reassurance that you’re not smoking those expensive 300B’s. It’s very easy with those large four pin sockets too!
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Hi Aaron:
One of my Elrog 300Bs died on me too. The other one tests low. I thought about buying a newer pair because they are supposedly more reliable/robust but in the end didn't want to get burned again (pun intended). Too bad because I thought they were the best sounding 300Bs I have ever heard. Even a bit better sounding than my 1998 re-issue WE 300Bs.
I just sold those 1998 WE 300Bs with an eye towards buying a new pair of WE 300Bs when they are released this fall. I wouldn't have sold the old pair if I wasn't 100% convinced that the new ones are coming back soon.
Back to the original topic of this thread, I just measured the 2nd amp and while the results were good, not quite as close to the manual numbers as the first amp (manual numbers / my results):
A1 74.1V 75.1V
A2 428V 426V
A3 0* 91mV
A4 69.2V 70.2V
*Close to zero
A3 was interesting. It started at 55mV and as the amp warmed up, it rose to a high of 91mV. I measured it one last time and the result was 86mV. I know this is a very low number and not anything to worry about, correct? Thanks!
Gerry
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Those are still healthy numbers.
Are you using the stock coupling caps?
~100mV isn't particularly concerning but still probably something to measure again in 6-12 months.
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What's this about WE 300B's being brought to market this fall? Is the information reliable?
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Are you using the stock coupling caps? ~100mV isn't particularly concerning but still probably something to measure again in 6-12 months.
PB - Thanks for answering my question. See the attached photo to answer your question.
Faskenite - Yes, very reliable information. These two links will provide all the information you need:
http://www.westernelectric.com/news/the-return.html (http://www.westernelectric.com/news/the-return.html)
https://www.facebook.com/WesternElectric/ (https://www.facebook.com/WesternElectric/)
Gerry
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Thanks for the links Gerry. There have been a few false alarms over the years. During which my 1998 WE’s have continued to work just fine!
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Hi:
It's been over a year since I took the original measurements and (as per PB) I was overdue to measure them again. Also, I have a pair of expensive 300Bs coming tomorrow and wanted to make sure they will not be stressed (more on that below). The A/C measured at the outlet was 120.7V. Here are the measurement results (Manual Numbers / Paramount #1 / Paramount #2):
A1 74.1V 77.5V 77.4V
A2 428V 433V 438V
A3 0* 22.0mV 21.8mV
A4 69.2V 72.8V 72.7V
*Close to zero
The only significant difference from my measurements over a year ago was that one of the amps measured approx. 91mV on A3. Today it was lower and much more consistent with the other amp. I have no idea why it's significantly(?) lower then the original test.
As I posted on the Audio Asylum, I'm #1 on the WE 300B pre-order list. After waiting over a year (PB you were right), I spoke with them last week. They are having glass issues but supposedly are getting closer. Here's my take on this - I ordered a pair of Takatsuki TA-300Bs last week from Parts Connexion. Enough said. Given the measurements listed above, am I good to go? Thanks!
Gerry
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The little bit of voltage that you had at pin 3 could indicate a tiny bit of gas perhaps that the getter has absorbed.
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@Gerry - I noticed from your photo that you've installed a V-Cap on what looks like a shunt regulator board, presumably in place of a stock Dayton Audio or similar. Did you notice any sonic change as a result?
@PB or @PJ: The fact that BH uses films caps on its shunt reg boards suggests to me that either (a) the cap is in the signal path, and/or (b) there is need for some property of film caps in this position (e.g., low ESR). Is it possible to explain the choice of a film cap for the shunt reg in layman's terms?
many thanks, Derek
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The film caps were something we already had in stock. Low ESL would be desirable for that cap.
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Many thanks PB. So I take it that any film cap with low inductance having the spec'ed capacitance will do.
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PJ will certainly weight in on this as well. The impedance of an electrolytic capacitor is not well enough behaved to function well in the high frequency compensation network for the regulator.
I haven't done any analysis on how critical this is, but since PJ has not specified a ceramic cap for that position, the situation is unlikely to be all that dire.
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@Gerry - I noticed from your photo that you've installed a V-Cap on what looks like a shunt regulator board, presumably in place of a stock Dayton Audio or similar. Did you notice any sonic change as a result?
many thanks, Derek
Hi Derek:
I purchased my Paramounts from the son of the original owner/builder. Sadly, his father had passed away. Both amps already had the large, upgraded Mundorf (coupling?) cap installed. Also, one of the amps already had the two smaller (.01uF?) V-Caps installed and the other amp had one. It appeared that the father had installed that second V-Cap in one of the amps but passed away before he got around to doing the other.
I didn't know the technical reason for upgrading those two smaller caps but in order to make the amps identical, I purchased another V-Cap and had it installed at the same time I had the v1.1 soft-start upgrade installed. Now that you know the background story, the answer to your question is that I don't know, I always heard the amps this way.
Gerry
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The cap is part of an RC network that maintains the low impedance of the shunt reg at high frequencies; without that network the impedance rises and becomes inductive. The values depend mostly on the voltage; at around 300 volts the corner frequency is around 10kHz so the cap is important above that frequency.
Therefor, in theory it should be well-behaved (i.e. with low ESR and ESL) at high frequencies. Initially, I did not expect it to be audible because it's dominated by the resistor except above 10kHz, and because the regulator itself is isolated from the tube by a very high impedance current source plate load. I included it because it should improve the stability margin of the circuit.
Of course, theory is limited in its ability to predict subtle effects that millions of years of evolution have made quite audible. Initially I doubted that it would be audible, but we tested this by substituting a Russian mil-spec teflon capacitor and were startled to find that it did make a small but audible improvement. So I spec a polypropylene capacitor, same as we use for coupling caps.
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Many thanks all.
@PJ: your comments are doubly helpful. Your observation that teflon caps produced a small but audible changes gives me something to play with without having to learn any new math ;D - I have a couple of 0.1 uF russian teflon caps kicking around. Whereas your points about the functioning of the rc network will require some reading and new math. I quickly looked up rc series networks and was met with discussion of phasors and complex numbers - I haven't yet ventured into this area in my learning. But leaving out phase, I think I mostly get how the inductance and capacitance of a component varies with frequency - so that mostly makes sense. But I've yet to make sense of how the shunt reg circuit works - I need to read up on what a LM/LT431 does and how it does it. More late reading! Many thanks.
cheers, Derek