I was right that a .001MFD cap is a 1000mmfd or 1000pf cap
BTW, the seller who provided that chart (justradios) is a good guy to deal with- one of my regular sources.
6BQ5 (EL84) PP amps that I have seen usually have output transformers with an Raa of around 8K, but sometimes they can go as low as 6K which might be stretching things a bit for the 6BM8. Checking out a schematic first might be a good idea.
Another consideration would be output transformers from an ECL86 PP amp, less watts but still enough for the 6BM8's.
As far as new output transformers go, I have used the Hammond 1609's (Raa=10k) with good success in 6BM8 pp amps, although I think Edcor would also be a good choice.
HTH Bill.........
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BTW, the seller who provided that chart (justradios) is a good guy to deal with- one of my regular sources.
I bookmarked the chart and I will revisit it soon. I am taking care of domestic issues right now. you know, cleaning the apartment, paying bills etc..
A thread on another ECL82 amp (based on a mullard)
http://www.diyaudio.com/forums/tubes-valves/184359-mullard-404-ecl82-amp.html
dave
http://www.diyaudio.com/forums/tubes-valves/184359-mullard-404-ecl82-amp.html
dave
I started buying the parts for this project. I call it the SAF-24-Next Generation. the 6ca4 was a bit than I expected. I got a good deal on the 5u4gb that the pdf shows should be just as good only now I need a 6.3, 5, and a 230 center tapped supply. I found a hammond from Antique Electronics Supply that has the voltages and grid bias take off. I also found a few nice transformers on ebay that have the ht at 270-0-270. One of them is a toroidal power transformer. I know nothing about toroidal transformers vs the standard iron core units. which are more efficient?
I bought 10 9pin ceramic sockets for about $12 from China and 3 Octal sockets from China. (never know if you need spares) and a matched pair of 12ax7 tubes.
I got the parts list organized and already started buying parts. Next month. its resistors and capacitors.
I haven't bought the 6bm8 tubes yet.
I bought 10 9pin ceramic sockets for about $12 from China and 3 Octal sockets from China. (never know if you need spares) and a matched pair of 12ax7 tubes.
I got the parts list organized and already started buying parts. Next month. its resistors and capacitors.
I haven't bought the 6bm8 tubes yet.
Thanks for the heads up. I guessed right on the 150ma. but the original schematic shows a 230-0-230 output. That isn't one of the voltages of the unit I see on Ebay. I do know how to drop the voltage using power resistors, If I really had to.
I know nothing about this simulator. does it work under Linux or MacOs 10.4 (Tiger) Does it come with source code that can be compiled on either?
Worse comes to worse, I will just have to test it on the bench. I am building the system in sections.
Don't know if it's available on any other system other than Windows.
There is quite a good discussion on the design of power supplies in the early parts of the Baby Huey thread. Although the aim is for a B+ of 300vdc and a current of 200ma the principles should prove useful to your own design.
www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey.html
HTH Bill
There is quite a good discussion on the design of power supplies in the early parts of the Baby Huey thread. Although the aim is for a B+ of 300vdc and a current of 200ma the principles should prove useful to your own design.
www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey.html
HTH Bill
Looking at my original schematic. looks to be two b+ results. what are the voltages? What about the grid bias generated by the half wave rectifier diode that connects to the bias tap at 26.5v of the transformer?
I am still looking for the best, least expensive, parts that will stll give hgh quality results.
I am still looking for the best, least expensive, parts that will stll give hgh quality results.
I made a goof. Thank god I caught it before I started building
. Yes,it is 300V plate voltage for the 6bm8 tubes. and it is the same for the 12ax7s so... When building the PS. (the amp is being built in sections.). I must make sure to use a loaded PS and adjust the voltage either after the rectification phase for 300v or pick a smaller voltage transformer(there are good deals on a 200ma 275-0-275 w/6.3 4A and 5V 3A toroid from Canada. Not sure if the filament supply needs more current for all those 6.3 filaments I may put the 12ax7s on their own filament transformer and the main amp on the big transformer.. I guestimate that the grid bias after the diode (original was a selenium) should be -24v (could be wrong though.
It's only a goof after you've bought the wrong thing and I'm not sure you have. Now that I 'm looking at the ACTUAL drawing.( there's a few 6mb8 threads at the moment - my excuse) I can see clearly the 230-0-230 spec of the transformer and the grid tap.
Have to check but 300vdc on the plates is to the top end of the 6bm8, I have an amp running at 210vdc. A quick run of your psu circuit with Duncan gives 235vdc at plate and 165vdc at the screens of the pentode. Perhaps someone else can verify ( Boywonder are you out there?).
As for the 12ax7's these may be rated for 300vdc or more but IIRC, 150 to 200vdc is more common. Again second opinion much appreciated
Have to check but 300vdc on the plates is to the top end of the 6bm8, I have an amp running at 210vdc. A quick run of your psu circuit with Duncan gives 235vdc at plate and 165vdc at the screens of the pentode. Perhaps someone else can verify ( Boywonder are you out there?).
As for the 12ax7's these may be rated for 300vdc or more but IIRC, 150 to 200vdc is more common. Again second opinion much appreciated
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Right, thats the max of both tubes. Again, the 150ma at 230-0-230 transformer at 150ma is the problem. That is. I cannot find one inexpensive at Ebay. Antec has one (Toroidal style) as does Edcor and Hammond (Classic style). I want to build a PS with some ability to allow me to upgrade my design if needed. I am on disability and a fixed income so. I need a ps that I won't outgrow too quickly. Ditto with the output transformers.
Given your best guess. I can hazard a guess that given a 275-0-275 output transformer that I can get about 285-290vdc. That means I need to drop 50vdc. that would mean a 330ohm 10 watt wirewound resistor. Now for the grid bias dropping resistor. my calculator shows 100ohms at 10 watts to bring 275v down to 25v for for the silicon diode. Might as well create a coffee cup warmer on this thing and put that waste heat to use.
One Ebayer Canadian parts supplier. has a 160ma toroidal power transformer from Tomiko for about $49 250-0-250 160ma. He says it is running his 4 6bq5 tubes and his 2 12ax7s well, in pp mode without getting hot. It is closer to the original 230-0-230 but I am really am leery that the 3A 6.3 filament supply is a bit low I like to have the extra juice in the event that I want to add to the system design.
Given your best guess. I can hazard a guess that given a 275-0-275 output transformer that I can get about 285-290vdc. That means I need to drop 50vdc. that would mean a 330ohm 10 watt wirewound resistor. Now for the grid bias dropping resistor. my calculator shows 100ohms at 10 watts to bring 275v down to 25v for for the silicon diode. Might as well create a coffee cup warmer on this thing and put that waste heat to use.
One Ebayer Canadian parts supplier. has a 160ma toroidal power transformer from Tomiko for about $49 250-0-250 160ma. He says it is running his 4 6bq5 tubes and his 2 12ax7s well, in pp mode without getting hot. It is closer to the original 230-0-230 but I am really am leery that the 3A 6.3 filament supply is a bit low I like to have the extra juice in the event that I want to add to the system design.
4 6bm8's + 2 12ax7's need
(4x0.78) + (2x0.3) = 3.72 amps - so you should get away with 4 amps.
If you can't source a cheap trannie with the correct grid tap then you could always get a second trannie to provide this. The current draw should be very small so a cheap small one might do.
ps I'm still reading your last post
Yeah, I know I can. I have seen 24v transformers very inexpensively. The problem is the space factor.
Does it have to have a centre tap? - you can still use your 5u4gb and 2 diodes for full wave rectification.
180ma+ would let your next build be 4xEL84/2X12A*7 of which there are many good circuits on this site. Output transformers between 8 to 10k are ok for EL84's but wouldn't want to go below 10 watts.
In the original schematic there is room for improvement in the psu ripple filtering. This gives you further scope to reduce your B+. Using dropping resistors to reduce B+ is just one option.
I think it's negative as well but need to get that sign right.
How many volts at 180ma do you recommend? Yeah, I am thinking that idea too.
As for the ripple. Good idea. I remember when I used to build half wave solid state rectifiers I would use a 2200uf in paralle with the output after the rectifier diode. I don't know if that would be practical in this application as the output was always a bit higher than the pre-rectified transformer output. right now, I am trying to implement the ps as it was designed with the change from the 6ca4 to the 5u4gb, which I got on Ebay (good condition used) fairly inexpensively.
I did say minus 24 volts. I am aware it is negative.
As for the ripple. Good idea. I remember when I used to build half wave solid state rectifiers I would use a 2200uf in paralle with the output after the rectifier diode. I don't know if that would be practical in this application as the output was always a bit higher than the pre-rectified transformer output. right now, I am trying to implement the ps as it was designed with the change from the 6ca4 to the 5u4gb, which I got on Ebay (good condition used) fairly inexpensively.
I did say minus 24 volts. I am aware it is negative.
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