Erik Mandaville Posted July 31, 2003 Share Posted July 31, 2003 Chris: I'm not going to be posting in the near future, but consider having Leo check the that voltage on the 5687 heater supply. If the heater pins on the tubes are difficult to access for measuring, he can just take a voltage reading across the rectifier -- Leo knows what he is doing! If you all find it's up around 7 volts, or so, a 1 ohm, 5 watt resistor will put things about right again. The supplies for heaters are sometimes intended for multiple tubes, not just one. A natural voltage drop would take place in such a case. But we have just one little fella to heat, and it's better to get that voltage as near to spec as possible. With 1 ohm in place, my heaters are now at 6.4 VDC, Which is close enough for me. When I get motivated again, I may bring the voltage down even further, to hover at around 6VDC. If Leo does this, also install another filter capacitor AFTER the dropping resistor. I don't know what Jeff put in your amps, but a 10,000mfd. (10-16 volts)would work fine. Some people will put the dropping resistor on the AC side of the rectifier (my Moondog schematic has this), but it's really more correct to do it after the rectifier, in the same fashion the B+ voltage is done. Erik Quote Link to comment Share on other sites More sharing options...
Chris Robinson Posted July 31, 2003 Share Posted July 31, 2003 Thanks, Erik ... I'll review with Leo and Jeff. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 31, 2003 Author Share Posted July 31, 2003 Jeff knows about this, Chris. He and I have been communicating a great length, lately...but absolutely, I would do the same thing if I were you! Erik Quote Link to comment Share on other sites More sharing options...
Chris Robinson Posted July 31, 2003 Share Posted July 31, 2003 ---------------- On 7/31/2003 9:21:03 AM Erik Mandaville wrote: Chris: I'm not going to be posting in the near future ---------------- Erik, just curious on your language here. Are leaving the board or just going on vacation for awhile? Hope it's the latter. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 31, 2003 Author Share Posted July 31, 2003 Thanks Chris -- that was nice of you to say. Just need to take a break and get some serious listening in, which will also help me get ready for school. Teaching can be stressful, and so I just want to take some time for myself and enjoy these wonderful new amplifiers. There is something else in the works, which I'll post here in a minute. Quote Link to comment Share on other sites More sharing options...
leok Posted August 1, 2003 Share Posted August 1, 2003 I went on a small hunt for heater tolerances. In a Svetlana databook I found 6.3V +/- 0.6V. I guess that puts 7V clearly out of the recommended range. Chris, I'll take a look at those voltages and add the suggested fix. Erik, did the additional capacitance reduce noise, or is it just a matter of principle? Chris, do you have a spare amp for listening to toons while your SETs are awaiting the checkup? leok Quote Link to comment Share on other sites More sharing options...
Chris Robinson Posted August 1, 2003 Share Posted August 1, 2003 Leo, thanks. To your question, negative. No stand-by capacity. These amps sound so frikkin' incredible I can't even imagine there's room for improvement, but bring it on. I had three sales managers in the house today (two of which were Bose fans), and they asked for an audition of both systems. They were blown away and left with a "to do" list. Quote Link to comment Share on other sites More sharing options...
edster00 Posted August 1, 2003 Share Posted August 1, 2003 Chris, I could send you a loaner amp to use while Leo is tuning up your amps if you would like (my Monarchy SM-70). It isn't tubes but it is a nice little amp in its own right. Any idea on when you might be coming down this way? Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted August 1, 2003 Author Share Posted August 1, 2003 Leo, Chris, Ed -- any of you guys! Let me get into this early tomorrow morning. Quote Link to comment Share on other sites More sharing options...
leok Posted August 1, 2003 Share Posted August 1, 2003 Chris, This isn't a sound improvement, just an improvment in expected time to failure. I have a P6D you can borrow if this takes more than a few minutes. leok Quote Link to comment Share on other sites More sharing options...
leok Posted August 1, 2003 Share Posted August 1, 2003 A few additional points: Jeff Lessard pointed out that the heater voltage is within the specifications I mentioned. I doubt there is an issue here .. just a point or two of concern. Chris, I'm sure you can continue to use your amps, and at some convenient time we can check the 6.3V heater voltage. leok Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted August 2, 2003 Author Share Posted August 2, 2003 From what I have learned, a little variation in voltage to heater/filament supplies is acceptable. If voltages are too low, though, there may be a chance for limited emission, which can both reduce tube life and compromise performance. Overly high voltages (mine were in the range of 7.2VDC)can cause stripping or evaporation of cathode material and also shorten the life of the tube. Fortunately, 5687s are comparatively inexpensive tubes, so replacement is not a big deal. Jeff's schematic specifies a 7,000uf in the filter for the rectified heater supply. I'm sure that value is totally adequate, but I just found many more 10,000uf capacitors in lower power ratings (9-16 volt range) than I did 7,000uf caps. A little extra capacitance is not going to do anything in this case. But yeah, Leo, you're right about the extra capacitor. It is in parallel with the load, and can maybe help a little with noise after the dropping resistor. If you look at the Horus schematic, you can see a similar situation in the B+ rectifier circuit: The 1.5uf input cap raises the voltage off the rectifier (I was utterly amazed at the strong reactance with such a low value capacitor -- I am using a 1uf cap in that position), and the smoothing chokes are in series with the load, with a filter cap (in parallel) between each choke. So, I'm just using 2 single 10,0000uf capacitors with a 1 ohm (5 watt) resistor between them. And I'm sure it would work fine without the extra capacitor -- which means I guess I am partly doing this out of principle, and because it's the way I have most often seen it done. The Moondog uses a series dropping resistor on the AC side of the 6SN7 rectifier -- kind of a brute force approach to the problem. It works, too. Actually, that is the case with the older c. 1998 (1999?) schematic. I think Kevin Cut Throat's more recent schematic uses the exact arrangement I mentioned above -- two 10K caps with a dropping resistor between them. The simple math I did for the power resistor actually came out to something more like 1.1 or 1.2 if I remember correctly. I just grabbed the first 1 ohm resistor I saw, and my heater supply is now 6.4 volts. Close enough! 5 watts is maybe just a little generous, but even that value gets warm. Works fine, though. Jeff suggested the high voltage as being perhaps due to the differnce in AC line voltage between here and Canada, which makes sense. It may also be partly due to the possibility that most filament supply transformers (or secondary windings) are often used to heat a few tubes rather than just one. That would probably cause a voltage drop because of the extra load, placing the average voltage closer to 6.3. So, That's the scoop with that! If you take the voltages on Chris's amps, I am very interested to see how they compared to mine, B+ voltages, too! You all have a great weekend, Erik Quote Link to comment Share on other sites More sharing options...
Chris Robinson Posted August 2, 2003 Share Posted August 2, 2003 ---------------- On 8/1/2003 5:20:53 PM edster00 wrote: Chris, I could send you a loaner amp to use while Leo is tuning up your amps if you would like (my Monarchy SM-70). It isn't tubes but it is a nice little amp in its own right. Any idea on when you might be coming down this way? ---------------- Ed, thanks for the offer. I think Leo and I can work out a time together to get things checked out in one session. My Atlanta trip will be nailed down this week so I'll be able to give you a definitive date then. I'm not sure how much time I'll be able to carve out (with business dinner, etc.) but I'm sure we can find time for an hour of listening! Will be fun to meet you (if you're not on vacation)! Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted August 2, 2003 Author Share Posted August 2, 2003 Chris: As Leo indicated, this is not something that has to do with the sound of the amplifier, per se.' It's a power supply issue that is mainly intended to keep the tubes within a fairly close proximity of the published operating parameters -- which in my case was not close enough for me -- I'm a picky sort of so-and-so! Unlike the 2A3, the 5687 is not a directly heated tube, and DC is used on the heaters, so chances of induced noise is going to be really small. Your amps are completely fine to use -- enjoy em and have a good weekend! Erik Quote Link to comment Share on other sites More sharing options...
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