I started an 811 SE amp last fall when I found some 811s at a meet... It's been thru 4 iterations so far, and the only thing left from the original schem is the 811!!
I'm using a 10A 6.3V FT and a 25A 50VDC bridge with 2x 22000uF caps, which gets it dead quiet, but the voltage is lower than I'd like (5.85VDC)... The amp sounds very good and is running on the breadboard with the last iteration for teh L channel, and the 3rd for the Right... Needed two channels running to load the PS to fine tune it ...
I am considering using a separate FT for each 811 heater, to bring the V up, but not sure if its really necessary, as the Vp is around 390-400V, which is pretty low for this tube... Grid is about 24-26VDC...
Anyone still working with 811s? What did you do to nail down the heater voltage? I'm not too keen on using a lot of SS devices, but open to any input...
Thanks in advance...
I'm using a 10A 6.3V FT and a 25A 50VDC bridge with 2x 22000uF caps, which gets it dead quiet, but the voltage is lower than I'd like (5.85VDC)... The amp sounds very good and is running on the breadboard with the last iteration for teh L channel, and the 3rd for the Right... Needed two channels running to load the PS to fine tune it ...
I am considering using a separate FT for each 811 heater, to bring the V up, but not sure if its really necessary, as the Vp is around 390-400V, which is pretty low for this tube... Grid is about 24-26VDC...
Anyone still working with 811s? What did you do to nail down the heater voltage? I'm not too keen on using a lot of SS devices, but open to any input...
Thanks in advance...
I have built a lot of 811A/572 amps PP and Se; i used two 5 amp 6.3 volt winding's, with 33000 uf caps 50 amp bridge for the PP .
Mostly the voltage ended up too high so I rewired with thinner wire or Resistors if the voltage was a little low just added Schottky doides to the 50 amp bridge. I have 105Db speakers and even up close cannot hear anything. I have used regulated DC but to me is not needed.
I prefer PP for these tubes, for Se prefer 805's One problem with the 811 and other high Mu Zero bias tubes is the internal resistance can be as high as 20 ohms not very good with modern poorly damped speakers tooo much boom. Some people of course love the boom.
Phil
Mostly the voltage ended up too high so I rewired with thinner wire or Resistors if the voltage was a little low just added Schottky doides to the 50 amp bridge. I have 105Db speakers and even up close cannot hear anything. I have used regulated DC but to me is not needed.
I prefer PP for these tubes, for Se prefer 805's One problem with the 811 and other high Mu Zero bias tubes is the internal resistance can be as high as 20 ohms not very good with modern poorly damped speakers tooo much boom. Some people of course love the boom.
Phil
I used individual schottky 16amp diodes. With where the filament is connected, you will get a bit of crosstalk between the channels if you use one filament transformer.
The schematic is rather squished.
The schematic is rather squished.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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Thanks for replying,,, Are you using one winding for each tube, or a pair?
I have two matching 10A 6.3V FTs, but would like to just use one, if I can to save space,,, the caps are pretty big physically... I see they will run a little high (6.6VDC) without resistors, with a tx for each tube...
Never used Shottky diodes, how will adding them raise the V?
I'm happy with the way the amps sound, just trying to dial in the heater supply a little tighter...
I have two matching 10A 6.3V FTs, but would like to just use one, if I can to save space,,, the caps are pretty big physically... I see they will run a little high (6.6VDC) without resistors, with a tx for each tube...
Never used Shottky diodes, how will adding them raise the V?
I'm happy with the way the amps sound, just trying to dial in the heater supply a little tighter...
Schottky barrier diodes have a lower on voltage, where si generally runs 0.7 to a little over a volt the MBR1635 (one I found at mouser, don't remember what I bought) has a voltage drop of 0.5 at 10 amps. Find the data sheet for the ones you bought and compare. A MUR1610 (general purpose ultra fast recovery), also rated at 16 amps, drops 0.82 volts at 10 amps.
HA,,, I have a black cat also... Haven't noticed crosstalk... I could try building a Shottky bridge, never used them tho... Maybe using both FTs may be the best way to do this... then I can just use the bridges I already have, if it will all fit...I used individual schottky 16amp diodes. With where the filament is connected, you will get a bit of crosstalk between the channels if you use one filament transformer.
The schematic is rather squished.
What did you use for OPTs? The schem I started with calls for 3.5k/10W, I was thinking more like 5k,,, B+ is similar to yours...
Thanks...
Edcor's GXSE15-8-3.5K. In 2013 it cost me $96.97 for both shipped.
If using a 6.3 volt 10 amp filament transformer then it's a little under powered for both; 10 X 0.62 = 6.2 amps. The 0.62 is the derating for rectifying and filtering. Google "Design Guide for Rectifier Use" from Hammond.
That big grey transformer in the back is for the filaments, it's rated for 2 X 8 amps.
If using a 6.3 volt 10 amp filament transformer then it's a little under powered for both; 10 X 0.62 = 6.2 amps. The 0.62 is the derating for rectifying and filtering. Google "Design Guide for Rectifier Use" from Hammond.
That big grey transformer in the back is for the filaments, it's rated for 2 X 8 amps.
The bridge I used is rated at 1.7V forward drop, with the 10A FT and 2 tubes on it... Starts out cold at 6.3-6.4 VDC, but after 5 minutes or so settles to about 5.8... amp sounds fine, but it may be a little low...
No, 3.15-0-3.15 tap... an 8V tap would be perfect...However,I do have two matching FTs...
I was going for the art deco look. That's walnut I had on hand, and some other veneer I got off ebay. I never used veneer before, cut it with a paper guillotine, worked alright.
Those are Chinese 811s, they sound fine, I also have 4 Cetron 811As.
If it starts off good and goes down, you're probably overloading the filament transformer. Hammond has a 185E12 that's 2 X 6.3V at 6.3 amps. You can parallel them together for 12.6 amps. Mouser has it for $26.70. It's pretty small, but not very pretty. Might be cheaper just to use both of the 10 amps you have.
Great info!!! I think we have the answer now,,, at 4A each, the filaments are drawing almost 2A more than Trans is rated... So, two separate filament supplies will allow the Tx/bridges to run cooler, with no more fans,,, that should eliminate any crosstalk, if it were to be a problem...
I was thinking Edcor or Transcendar... Seems the Trancendar 10W OPT is bigger than Edcors 15W, and according to Jeri at Transcendar, should be fine,,, Theres a pretty big price gap, tho... I don't have experience with either company, however, Edcor wasn't interested in discussing the project, and then there's the "build/shipping time"....
Thank for all the info...
Yep... and I have matching caps and bridges!!! Hope I can fit them in teh chassis.
I like the inlay in your base... Mine is more traditional, not finished yet, tho...
A choke input filter lets you use the transformers to their rated current and reduces stress on the transformers. 6.3Vrms x2 in series should allow you your 8V plus a little to drop across the resistance of the chokes.
Chokes at the output of the filters (without a subsequent capacitor, just filtering into the resistance of the filaments) should allow you to use one supply for both.
Chokes at the output of the filters (without a subsequent capacitor, just filtering into the resistance of the filaments) should allow you to use one supply for both.
Not quite clear on what you mean? Won't a choke add resistance to an already low Voltage supply?
I just happen to be building a high current supply myself, so.. What I suggested may be more difficult but can make for a good supply. The chokes provide reactance required for the filtering with less resistance than it would take for that kind of filtering using resistors alone.
In addition, the second one might assist in isolating the supply from your filaments to reduce signal currents going through the supply.
BTW this supply isn't for filaments but I do my filaments this way as well. I needed to wind one of the chokes, and they're not small.. but I'm happy with the result.
In addition, the second one might assist in isolating the supply from your filaments to reduce signal currents going through the supply.
BTW this supply isn't for filaments but I do my filaments this way as well. I needed to wind one of the chokes, and they're not small.. but I'm happy with the result.
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