One other point I should make is that my power transformer is designed for 230v mains. Where I live in Indonesia, the mains voltage is nominally 220v but the actual measured voltage is usually between 190v and 200v! This gives low B+. For triode operation, the EL34s should be getting at least 400v plate-to-cathode but they never do in practice: it's more like 380v, as shown on my circuit. The heaters are also under-powered.
The low mains voltage means that my available power OP is lower than it should be: about 13.5w instead of 16w. I daresay the tubes will live longer but I also think it might sound better if the mains voltage were 220v, as it should be. I hope the power in your part of the world is better!
The low mains voltage means that my available power OP is lower than it should be: about 13.5w instead of 16w. I daresay the tubes will live longer but I also think it might sound better if the mains voltage were 220v, as it should be. I hope the power in your part of the world is better!
where i live, the utility voltages are rock stable at 230volts day or night.
Ray_moth,
just to confirm, the polarity of your ouptut transformer from drawings is, top el34 to start, bottom el34 to finish, right?
thanks
Ray_moth,
just to confirm, the polarity of your ouptut transformer from drawings is, top el34 to start, bottom el34 to finish, right?
thanks
Tony said:
Wow! we have swings from 170V to 320V with short peaks to 340V and brown outs to 150V. One night when I was single all of a sudden bulbs started blowning and the air con started acting nuts. I hit the mains switch and carefully measured the voltage. It was 380V! I was noew to India then. When I informed my friends they laughed. One of them has measured 410V
It is so bad here we have a 1.5KVA UPS in each room and connect essential stuff like telephones, fridge, computer, a few lights to these.
Tony:
Yes, that'd be right. B+ goes to centre tap, which is consistent with what you say.
Navin, what you report about your mains power is amazing!
Yes, that'd be right. B+ goes to centre tap, which is consistent with what you say.
Navin, what you report about your mains power is amazing!
ray_moth said:
If I were to use a CCS for the EL34s, can I eliminate the 2 resistors between the coupling cap and grid stoppers to the bias pots, or do I still need a grid leak? I'm thinking of doing a very simple LM317 CCS, like in http://www.diyparadise.com/yhlmccs.html, do you think it is fine? I would like to keep things as simple as possible if it works! I think for the 6SL7, I will still need a negative rail, for the EL34s, I can ground the adj/output right?
Also for the -115V rail, I can do with less right? Just have to tweak the R17, 18 and 21 lower? I'm thinking of maybe -50?
thanks again ray_moth!
On no account can you omit the "grid leak" resistor. In fact, the manufacturer recommends a max. value and it's usually best to go below that. With cathode bias instead of grid bias, you can safely go to 0.5 Meg with EL34s.
AFAIK, the LM317 is generally considered to be a poor device to use for a cathode CCS, mainly because of its limited frequency range. I guess you would not need a negative line with a SS CCS cathode bias for EL34s but I have no experience in this area.
Bear in mind that this arrangement (shared CCS in cathodes) forces the tubes into class A, because the sum of the two cathode currents must always be the same. Is this what you want?
The reason for my -105v rail is to keep the 6AU6 CCS happy. With a SS CCS, a much lower neg, voltage is sufficient. -50 volts will do, for all purposes, including grid bias for the EL34s if you use that.
Hello guys I have a really old schematic and I'm really confuse because I'm a "solid state guy" but I want also to learn tube amplification, there are many good designs out there ST-70, eicos, etc there are more but probably you guys seen them, here is the schematic of what I want to build, today I just find out that there are many way to connect the tube "PP" here is also the image of those configurations, I just want to know if this schematic will be just fine, I'm a newbie and at least I want to star with something simple then later on I can go to more advanced circuit like ST-70, what you think guys is ok this schematic? is from a 1959 RCA book "PDF". oh by the way I'm not looking for high wattage I'm looking for good response and good sound and not need to have the unit under stress to achieve that, just stable, longer live for tubes too. Sorry maybe I'm away from you guys topic I apologize in advance.
Regards
Juan
Regards
Juan
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These aren't entire different ways to connect a tube. These are just fancy ways to apply local feedback (Something not seen very often in solid state amps).
Like many others, you came here and already brought your schematic with you - fine 🙂 No flaws as I see so far in this circuit. But you may also look at those typical newbie amplifiers which use modern/easy available tubes.
oh? wow thank you sir I thought that the schematic might have an error, I be honest I'm new to this but I want to learn, I forgot to show the original schematic for the PDF files here, this are the original info from that RCA book. I just found one little detail on the schematic not really a big deal, I forgot a drawing for "no connection" between R11 and R16 is not big deal.
Regards
Juan
Regards
Juan
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