Does anyone have a good recent supplier for the Novar sockets? I got no response from emailing ESRC1 as per Tom's recommendation. After much Internet searching it appears these are hard to track down.
@tomchr - a suggestion that maybe you could buy a batch of these and offer them through your web store with the boards?
@tomchr - a suggestion that maybe you could buy a batch of these and offer them through your web store with the boards?
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Weird that ESRC doesn't respond. I'd try: www.vacuumtubes.net or eBay.
I generally avoid building inventory as it requires management. I'll see if I can find a good source.
Tom
I generally avoid building inventory as it requires management. I'll see if I can find a good source.
Tom
Thanks Tom, I'll try ESRC again as I just checked their contact details and there is a different email address on the "Contact Us" page from the one on their home page. I used the AOL address on the "Contact Us" page, so I'll give the other one a try.
Thanks Tom. No problem at the moment, as Stan has sent me a reply from the other email address.
I have the board and most of the parts I need to complete the build, minus the chassis. I was originally going to go with the 6LR8 version, but depending on your answers to my questions, I might opt for the 6GF7A version instead.
1. Is the output from the 6GF7A version enough to drive my speakers (98 db efficiency)
2. I purchased the 250V Antek tranny. If I used a voltage divider (using 5R and 20R resistors) to get that down to 200V, would that tranny work for the 6GF7A version?
3. If yes to question 2, what wattage would you recommend for the voltage divider resistors?
Thanks in advance for your help.
1. Is the output from the 6GF7A version enough to drive my speakers (98 db efficiency)
2. I purchased the 250V Antek tranny. If I used a voltage divider (using 5R and 20R resistors) to get that down to 200V, would that tranny work for the 6GF7A version?
3. If yes to question 2, what wattage would you recommend for the voltage divider resistors?
Thanks in advance for your help.
1. The SE spud on any of your options will give 2+ Watt, enough;
2. Just get a 200V 50VA toroid AnTek on evilBay, there are plenty;
3. Khe-m, let's calculate: P = V * V / R or 250*250/25 = 2,500 Watt. m-m-m, the AnTek trafo might not fit here. .. you could opt for a 2.5 KWa welding one, that's for sure, you will also need a 25A NEMA wall socket. ..and a plug ))
2. Just get a 200V 50VA toroid AnTek on evilBay, there are plenty;
3. Khe-m, let's calculate: P = V * V / R or 250*250/25 = 2,500 Watt. m-m-m, the AnTek trafo might not fit here. .. you could opt for a 2.5 KWa welding one, that's for sure, you will also need a 25A NEMA wall socket. ..and a plug ))
Hmm.... Shef, I don't completely understand your answer. I already purchased the recommended Antek power transformer for the 6LR8 version of the amp (Antek AS-1T250 100VA). What I want to know is if it would be OK to use that transformer with a simple voltage divider to get the 200V needed for the 6GF7A version of the amp instead of purchasing the Antek AS-1T200 100VA, which is the recommended transformer for the 6GF7A.
If it is possible to use the Antek AS-1T250 100VA, what should the wattage of the voltage divider resistors be?
If it is possible to use the Antek AS-1T250 100VA, what should the wattage of the voltage divider resistors be?
Eh, nowhere close.
Here is my estimation, as I don't have a schematic of this amp. I.e. take it for what it's worth.
250VAC rectified with SS with no load will result in 350VDC, give or take.
Assuming 120mA current draw (for both channels), 25V cathode bias, 35V drop over B+ filter & OPT, you're looking at 350-25-35=290VDC between plate and cathode.
You want to bring it to 200V. R=U/I=90/.12=750 Ohm in series with the amp. Actual Power=90*.12=10.8W. A resistor rated for 15W or more should be OK.
HTH
Just remember that the el caps have to be 400V rated.
I do not see a problem of operating them with 320 plate-cathode. I tried 6KY8s with 350, worked just fine. Since the OPTs are not on hands yet (I assume) a bit bigger primary impedance with lower quiescent can be perfectly fitted, I guess like 6K. Such, most likely will even sound better, with maybe 25% less of sound power.
I do not see a problem of operating them with 320 plate-cathode. I tried 6KY8s with 350, worked just fine. Since the OPTs are not on hands yet (I assume) a bit bigger primary impedance with lower quiescent can be perfectly fitted, I guess like 6K. Such, most likely will even sound better, with maybe 25% less of sound power.
Which tube are you talking about? 6GF8 or 6KY8? If 6KY8: in pentode, UL or triode mode? Did you draw up the load lines?
I'm in the process of building Tom's Novar Spud (6LR8) along with the Universal filament regulator and have a couple questions. I'm wiring the AS-1T250 dual 6.3v secondaries in series for 12.6v into a simple DC power supply. That should get me about 17.8v into the filament regulator which will then be brought down to the clean 6.3v needed for the heaters.
What I'm confused about is R21 and R22. These are meant to elevate the heaters to 30V per the documentation; isn't that a bit too much? Is there anything else I need to look out for when running the filament regulator?
What I'm confused about is R21 and R22. These are meant to elevate the heaters to 30V per the documentation; isn't that a bit too much? Is there anything else I need to look out for when running the filament regulator?
I'm pretty sure you were the one who sent me an email a few days ago. I've responded and I believe you settled on getting another transformer. For everyone's benefit, I'll answer your questions below.
As you can see in the spec table on my Novar Spud page, you'll get 2.3 W with the 6GF7A. That's enough for over 100 dB SPL at 1 m, assuming stereo operation. That's certainly loud enough for me. My typical listening levels for critical listening are around 80 dB...
A resistive divider is not a good option for a power supply due to the enormous amount of power dissipated in the resistors (as Shef described above). In addition, a voltage divider will have relatively high output impedance, which degrades the performance of the amp (think mushy bass and such).
The best option would be my 21st Century Maida Regulator. With its low output impedance, it provides the best operating conditions for the Novar Spud. I find the bass tightens up due to that. Also with its extremely low output noise, it cleans up the midrange and highs. But it is also more expensive than the default LC filter in the Novar Spud.
The second best option would be to get the AS-1T200 transformer from Antek. You might be able to squeeze by with the 50 VA version, the AS-05T200, with the 6GF7A. Just put the two heater windings in parallel for powering the Novar Spud.
You're welcome. I hope I've answered your questions in sufficient detail.
Tom (who's sitting in the morning sun in Fort Collins, CO midway through the vacation)
So now the supply has 750 Ω output impedance. Not my cup of tea. But you're right. It probably would work.
You're right that a 15 W resistor will in theory survive 10.8 W dissipated - assuming 25 ºC ambient. It'll reach 250-300 ºC under those conditions. This may be safe for the resistor but isn't safe for much of anything else. I generally derate power resistors by 3-5x. I'd use a chassis-mounted 50 W type with a heat sink for the application if I was to go that route.
Tom
The heaters are elevated to protect the heater-cathode interface in one of the tube sections. I don't remember if the elevated heater is necessary with all the three supported tube types, but it is necessary with at least one of them. The values I recommend will work for all three tube types, so I'd go with what the documentation says.
Just beware that the heater supply needs to be floating. If you're using regulators and such, make sure they're floating - i.e. not connected to ground.
Tom
Good question. I certainly did during the design phase. While the tubes did seem to conform roughly to the specs in their respective data sheets, I found that the measured performance of the amp as well as the sound quality was actually pretty bad at the operating points that would normally seem obvious from the characteristic curves. I did a fair amount of experimentation to get an amp that would sound good and measure well.
It's been quite a while since I designed the amp so the details escape me and my notebooks are at home. I do seem to have to back off from the max spec on the anode-cathode voltage with the 6GF7A to get the best performance.
Tom
Hi Tom,
Thank you for your answer, however, my loadline question was directed at Shef's post #111. Maybe you have a comment on running the amp at the voltages he is suggesting? Thanks!
P.S. Could you post a schematic? It would help the conversation.
Sorry, missed the question.
I tried 6KY8 with up to 350V. There was no intend to keep it that high, I just quickly test-rigged and auditioned different operating points, no load lines drawn.
I have an OPT with switchable secondaries (by Hammond) so I simply adjusted the quiescent current to raised B+ and then varied the plate load impedance. The trafo is triode mode only, the 2nd grid was connected to plate via 200E.
I recall 6-7K sounded very good, ran it like this for maybe half an hour, the tubes survived. I have 3 pcs by Sylvania top-tipped which I tortured, these played the die-hards on me.
Did not measure the output power drop, subjectively it was about a quarter less comparing to the more common/recommended mode, I was mostly curious about the sound quality, and I liked it better with higher B+.
After all I decided, well, if I wanna go higher B+ I just use EL34 etc.
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