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Old 27th March 2010, 11:15 PM   #1
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Default Too quiet on the Simple P-P front??

Haven't heard much lately from the "beta" SP-P's. I have a board and would start it but for a couple of questions....

In another post, George hinted that some resistor changes might occur on the parts list. If this is so with the EL84 version, I'd like to know what they might be.

I'd like to use an Edcor power transformer. They list a #XPWR008 = 120V / 600V (300-0-300) @ 200ma, 6.3V @ 4A, 5V @ 3A. Would the B+ end up being too low (5AR4 tube rectifier) to work well with the EL84? I don't really want to take the EL84's much past 325V anyway. I'm happy with anything that ends up putting out around 10WPC.

Any benefit (or detriment) to installing additional capacitor in the power supply? I ask because the motor run cap I added to my SSE made a large difference to the background silence of that amp.

Finally, am I to assume the feedback and UL / triode connections on the circuit board are configured the same way as on the SSE board? In other words, do you use jumpers on the terminals, if those options are not used?
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Last edited by neonthecat; 27th March 2010 at 11:27 PM. Reason: change to text
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Old 28th March 2010, 12:15 PM   #2
Ian444 is offline Ian444  Australia
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A few possible impending resistor changes would not put me off building a PCB. If you want to be on the bleeding edge, that is the tiny price you pay read the schem and build the amp. If George knew what the revisions were gonna be he would have posted them. 600V CT should get you more than 10W, that's what I am starting out with. Read the schem to get your connections right.
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Old 28th March 2010, 01:09 PM   #3
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Quote:
Haven't heard much lately from the "beta" SP-P's. I have a board and would start it but for a couple of questions....
I have been stuck at work lately until 7 or 8 PM most every night trying to get a new project approved. If it is approved that may become the norm. If not.......

One of the beta testers reported some distortion on scope traces in his amp with certain 12AT7 tubes (1 out of 3 JJ's and an EH or two). He was able to fix that by changing a few resistor values, but I can not duplicate this effect here. It is not clear whether the resistor changes he made improved the sound or not. His observations got worse as the B+ voltage was lowered and my 3 working boards operate from 200 volts to 400 volts without issue. He has sent me the offending tubes which arrived yesterday, but as yet I have not had any tube time. It is possible that these tubes are weak, but If a resistor value or two can be changed to make them work without compromising operation with NOS 12AT7's I'll will make a change to the parts list.

Quote:
read the schem and build the amp.
Go by the parts list on the web site. It is what I used to build the boards that I have here.

Quote:
I'd like to use an Edcor power transformer. They list a #XPWR008 = 120V / 600V (300-0-300) @ 200ma, 6.3V @ 4A, 5V @ 3A. Would the B+ end up being too low (5AR4 tube rectifier) to work well with the EL84? I don't really want to take the EL84's much past 325V anyway. I'm happy with anything that ends up putting out around 10WPC.
I have been using 2 different Hammond 300-0-300 volt transformers which are really 325-0-325 volts. They give me between 345 and 355 volts of B+ depending on the line voltage and time ao day (power line distortion increases in the afternoon). An Edcor should be closer to its rated voltage.

Quote:
Any benefit (or detriment) to installing additional capacitor in the power supply? I ask because the motor run cap I added to my SSE made a large difference to the background silence of that amp.
A P-P amp has much greater rejection of power supply noise than a SE amp by design, so that the motor run cap will not make as big of an improvement but you will still see some improvement in transient detail. I would say that the optional choke and cap were almost mandantory in the Simple SE. They are truly optional here. I don't use either in the amp that I have been using, but that might change if I had more efficient speakers.

Quote:
Finally, am I to assume the feedback and UL / triode connections on the circuit board are configured the same way as on the SSE board? In other words, do you use jumpers on the terminals, if those options are not used?
Yes, the amp can be jumpered into triode, UL, or pentode mode. It is expected that most amps will be connected in pentode mode. These are wired in a manner similar to the Simple SE but there are twice as many tubes and the jumper locations have moved. I haven't finished my Visio diagrams yet, but photos of pentode wiring have been posted here.
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Old 28th March 2010, 03:41 PM   #4
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Thanks George for your comments and help!
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Old 29th March 2010, 03:44 PM   #5
rknize is offline rknize  United States
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You can probably expect about 300V B+ with that transformer. My experience with Edcor so far is that they hit their mark under load. If you want to run B+ on the higher end, take a look at the XPWR131 (custom iron for my TSE...just don't use the extra taps). That should give you more like 330V.

If you plan to use any of the Russian EL84s, you might consider running a lower B+. My experience and the experience of many others on the Internet is that these tubes, which descend from the Russian military 6P14P, don't like more than 300V across them. The only way I was able to do it is to lower their screen voltage, but this increased the distortion numbers noticeably. 300V of B+ will run them at about 285-290V, which should keep them happy.

If you plan on sticking with JJs or maybe other real NOS EL84s, you are probably OK at the higher voltage. In fact, I have take the JJs as far as my Hammond transformer will go on the variac as they take it in stride. They seem to be tough tubes, they sound good, and they are the cheapest current production tubes to boot!
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Old 29th March 2010, 03:54 PM   #6
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Good info, Russ.
I have a quad of Electro Harmonix EL84 that are waiting for the SP-P. They seem to have a decent rep for being tough (should handle B+ around my target of 300V).
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