I am looking to build a tube amp for bass in a biamp system. The 813 looks extreemly interesting. I would like between 70-140wpc. I would like strong bass that is punchy. I found these links:
http://www.pmillett.com/813_se_triode_amps.htm
http://members.aol.com/analogengineer/813mat.htm
http://homepages.ihug.co.nz/~rwillis/alex/
http://home.zonnet.nl/horneman/813.htm
http://www.izzy-wizzy.com/audio/powamp813.html
When can i add a second 813 in parallel to double the output (only pushpull?)? Assuming PSU can handel it.
What do you think?
thanks
http://www.pmillett.com/813_se_triode_amps.htm
http://members.aol.com/analogengineer/813mat.htm
http://homepages.ihug.co.nz/~rwillis/alex/
http://home.zonnet.nl/horneman/813.htm
http://www.izzy-wizzy.com/audio/powamp813.html
When can i add a second 813 in parallel to double the output (only pushpull?)? Assuming PSU can handel it.
What do you think?
thanks
"Halve" means "divide by two" (just like paralleling any two equal resistances.) In this context, yes that's a lot. If you double the number of output tubes, your output transformer would have to present half the load impedance of the single-tube design, in addition to handling twice the power . Many transformers allow the use of a different tap to acheive the correct impedance; the power handling will probably be the chief issue, especially for low frequencies.
Reid
Reid
I did not realy say that right, when i said "plate resistance would change alot?" i was talking about all the values of resistors and capacitors changeing. Can i parrellel on SE? Say i wanted to parallel this scematic: http://homepages.ihug.co.nz/~rwillis/alex/813_se_2_schematic.jpg
I would use a 3K transformer?
I would use a 3K transformer?
I don't think using a beam power tetrode in SE parallel or not is going to net you the bass you are looking for. The output impedance even in the UL connection is going to be at least a couple of ohms relative to an 8 ohm tap, frankly I suspect higher than that. You would need of feedback to get a reasonable damping factor (say 10) This tube requires a lot of voltage drive as well and plate voltages of around 1KV for good performance.
Why not try something with a couple of parallel 6C33? Low Rp with a properly chosen transformer would allow for low/no feedback operation in SE.
Why not try something with a couple of parallel 6C33? Low Rp with a properly chosen transformer would allow for low/no feedback operation in SE.
Bandersnatch said:
He was asking for a 70-150W tube amp to power the bass in a bi-amped system. If you want that kind of wattage in class A, it's going to cost a lot in heat and weight. The subtle spatial and phase related cues that make music come alive are most important in the mid and upper registers. And it's hardest to maintain phase accuracy and low distortion figures as frequency rises. The differences between a good AB amp and a class A amp (both PP) would be much less than for mid-bass and tweeter. Cost vs. benefit. Spend your money where it does the most good.
Now, Ak didn't specify where he was crossing, but the fact that he's looking for that much power suggest that it's on the the lower end. Ak?
Sheldon
ak_47_boy said:
I don't think there is a normal. It all depends on the drivers and what you are trying to do. I have a quad-amped system. Shown here: http://www.diyaudio.com/forums/showthread.php?s=&threadid=69906&perpage=10&highlight=&pagenumber=1
In its current configuration, I'm using a DEQX and the tweeter and mids are driven by two different low watt SE amplifiers. These: http://www.diyaudio.com/forums/showthread.php?postid=883561#post883561 The tweeter is crossed over to the mids at 1100Hz, 48dB, digital filter.
The 15"ers and 12" sub are driven by one of these each side: http://www.diyaudio.com/forums/showthread.php?postid=862086#post862086 It's a design by one or our members, Mike Bittner.
The 15" is crossed over to the horn at 350Hz, 96dB digital. The 12" is crossed over to the 15" with a line level analog crossover I built into each stereo amp (so one stereo amp per side). This crossover is a phase perfect design from John Kreskofsky, at 80Hz.
I did it this way, as the DEQX only has three outputs and I needed three crossovers. On the lowest one, I only needed to get the crossover point itself done well. The remaining adjustment is taken care of by the room correction feature in the DEQX.
Sheldon
Sheldon said:
Well I read it a bit differently. If 70-100W is a reasonable window, then a pair of KT88's would be quite adequate. What he asked for was an 813 amp. 80-90 Watts is a reasonable expectation for a pair in Class A.
Class A offers a few advantages over AB, and a lot are useful when the load Z is changing at LF due to enclosure interaction. The load will stay a lot closer to a-a/2 for each of the valves. In AB you get a distinct transition to a-a/4 when you get the other tube cut off.
Also, considering that 100W will be giong into just the cathode heating for a pair, I don't think efficiency is a primary concern. I have just such an 813 amp on the way. First it is going to be a 4E27 amp...then the output TX gets switched and B+ increased and 813's plugged into the sockets. Who knows, maybe I will like the radial pentodes better...
cheers,
Douglas
Hey-Hey!!!,
There are a few limits to look at in such amps. A 20 cps lower limit is no simple thing. The combination of increasing phase angle from inadequate primary L and core saturation from not enough of it are both working agianst the project. The usual HF issues don't really apply as it will be used for LF only.
Anyway, I am going to run mine full range. I will be using the Citation II outputs for the first iteration. Next up is a specially modified S-271-S from Heyboer. The modified Peerless is 5k a-a v. the 3k2 of the Freed. I think they'll have no issue with the high idle current. Expected power is within their capability even if they don't have much margin. I may adjust the B+ a bit, but the plate TX is fed from an autoformer so it's quite simple.
There is a bit of PS experimentation to do as well. Henry Pasternack's Flywheel design is in the works for the 4E27 variant. I happen to have the bits laying about to build that deisgn to the same B+ as the standard choke input. As usual this is a science experiment, and it is my first big transmitting tube amp.
cheers,
Douglas
There are a few limits to look at in such amps. A 20 cps lower limit is no simple thing. The combination of increasing phase angle from inadequate primary L and core saturation from not enough of it are both working agianst the project. The usual HF issues don't really apply as it will be used for LF only.
Anyway, I am going to run mine full range. I will be using the Citation II outputs for the first iteration. Next up is a specially modified S-271-S from Heyboer. The modified Peerless is 5k a-a v. the 3k2 of the Freed. I think they'll have no issue with the high idle current. Expected power is within their capability even if they don't have much margin. I may adjust the B+ a bit, but the plate TX is fed from an autoformer so it's quite simple.
There is a bit of PS experimentation to do as well. Henry Pasternack's Flywheel design is in the works for the 4E27 variant. I happen to have the bits laying about to build that deisgn to the same B+ as the standard choke input. As usual this is a science experiment, and it is my first big transmitting tube amp.
cheers,
Douglas
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