Well, me being the broke, and incredibly cheap, “student” that I am......here's what I've been thinking of....
I want a mono PP tube amp for the horn section(active crossover system) of my "mono rig" which can be referenced in other threads of mine linked here
http://www.diyaudio.com/forums/showthread.php?s=&threadid=123024&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=122369&highlight=
Right now the horn is crossed over at around 1200hz(would like to do 800hz, but those modules for the Peavey xover seem to be getting kinda pricey on fleabay...might have to look in modding the “cans”(I have more than a few) if possible, or even just ditching the Peavey and building my own tube crossover.....but that’s ANOTHER thread). The horn is currently being amplified by half of a Crown D-150(yeah I can hear the screeching and gasps from here....that’s what I’m here for...the D-150 will be for subwoofer duties *only*, after I build the "horn amp" obviously).
Now comes the fun part…what I have been “thinking”.....here’s what I have in my "Parts bin" that might work……
I have a knight KN530 (mono EL34PP, good OP trans.....I think....probably should test that), but no power transformer. Finding a *cheap* direct replacement PT has yielded no results. From the spec sheet I “need” around a 350 swing.....which are relatively available on ebay......but there is another cheaper option that I have been considering......
I also have a Thomas Model A-1 “tone control” unit, that is an EL84 based mono unit also PP I think(don’t have a schematic….yet). Pictured here
And here
I haven’t taken any readings on the power trans for specs, but would assume that it has a typical EL84 swing of around 250v to 300v. The unit DOESN’T have filament power though, so I suppose that I would have to use a stand alone low power trans to supplement. I have a old "tube tv tuner" that might have one to "donate" to the cause.....
I was thinking that I could pull the power trans from the Thomas and use the output trans from the Knight and put together an EL34 mono PP amp(I have more than a few EL34s from my Dynaco ST-70 days) with a “decent” amount of power for a horn, even if not using the EL34s to their "full potential". I’m not going for ear bleeding noise, just good sound quality…..with an occasional cranked up song or rif…..
I still haven’t decided on a driver stage, though I do have a ton of 12au7 tubes.
I was also thinking of using the knight schematic as a starting point, as designing my own amp is still a bit “out of my league”. I realize that with a different PT, many of the component values will be different, but I feel fairly confident that I can “compensate”.
So….what should I do……stick with my above “ideal” plan and use the EL34s(much preferred), or step down to the EL84s, and basically just use the guts of the Thomas.
Should I copy the knight topography, or is their a better option?
Additionally, I am going to custom build my own chassis(actually two…one for the power, one for the output) so that it will fit behind(around...two triangle bases) the horn itself, as I am running out of room on my “platform”. I have a basic layout drawn up and all the components mentioned should fit just fine.
Any and all ideas or suggestions would be greatly appreciated…..
Thanks for your time…..
Nate
I want a mono PP tube amp for the horn section(active crossover system) of my "mono rig" which can be referenced in other threads of mine linked here
http://www.diyaudio.com/forums/showthread.php?s=&threadid=123024&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=122369&highlight=
Right now the horn is crossed over at around 1200hz(would like to do 800hz, but those modules for the Peavey xover seem to be getting kinda pricey on fleabay...might have to look in modding the “cans”(I have more than a few) if possible, or even just ditching the Peavey and building my own tube crossover.....but that’s ANOTHER thread). The horn is currently being amplified by half of a Crown D-150(yeah I can hear the screeching and gasps from here....that’s what I’m here for...the D-150 will be for subwoofer duties *only*, after I build the "horn amp" obviously).
Now comes the fun part…what I have been “thinking”.....here’s what I have in my "Parts bin" that might work……
I have a knight KN530 (mono EL34PP, good OP trans.....I think....probably should test that), but no power transformer. Finding a *cheap* direct replacement PT has yielded no results. From the spec sheet I “need” around a 350 swing.....which are relatively available on ebay......but there is another cheaper option that I have been considering......
I also have a Thomas Model A-1 “tone control” unit, that is an EL84 based mono unit also PP I think(don’t have a schematic….yet). Pictured here
An externally hosted image should be here but it was not working when we last tested it.
And here
An externally hosted image should be here but it was not working when we last tested it.
I haven’t taken any readings on the power trans for specs, but would assume that it has a typical EL84 swing of around 250v to 300v. The unit DOESN’T have filament power though, so I suppose that I would have to use a stand alone low power trans to supplement. I have a old "tube tv tuner" that might have one to "donate" to the cause.....
I was thinking that I could pull the power trans from the Thomas and use the output trans from the Knight and put together an EL34 mono PP amp(I have more than a few EL34s from my Dynaco ST-70 days) with a “decent” amount of power for a horn, even if not using the EL34s to their "full potential". I’m not going for ear bleeding noise, just good sound quality…..with an occasional cranked up song or rif…..
I still haven’t decided on a driver stage, though I do have a ton of 12au7 tubes.
I was also thinking of using the knight schematic as a starting point, as designing my own amp is still a bit “out of my league”. I realize that with a different PT, many of the component values will be different, but I feel fairly confident that I can “compensate”.
So….what should I do……stick with my above “ideal” plan and use the EL34s(much preferred), or step down to the EL84s, and basically just use the guts of the Thomas.
Should I copy the knight topography, or is their a better option?
Additionally, I am going to custom build my own chassis(actually two…one for the power, one for the output) so that it will fit behind(around...two triangle bases) the horn itself, as I am running out of room on my “platform”. I have a basic layout drawn up and all the components mentioned should fit just fine.
Any and all ideas or suggestions would be greatly appreciated…..
Thanks for your time…..
Nate
took some basic measurements
So after feeling a little lazy, I got motivated and tore into the A-1. Clipped all the stuff going to the power trans(including cap), set the multimeter to AC, hooked up power and got this
(2)Blue wires - 56vac
(2)Green wires - 7.68vac
(2)Red wires - 633vac....(woohoo)
(1)Green/yellow wire that was attached to chassis......didnt measure that at all.......not sure exactly what it does(center tap of some sort maybe???).
So yeah....no amperage readings, but I was apparently wrong about not having any filament power. Its been a few years since I got the unit.....I must of been thinking of another "project"......
anyway here is a pic of the carnage......
Obviously I was testing the cloth cover wires......
so what is the best way to get amperage specs on a tranformer such as this?
Thanks again.....
Nate
So after feeling a little lazy, I got motivated and tore into the A-1. Clipped all the stuff going to the power trans(including cap), set the multimeter to AC, hooked up power and got this
(2)Blue wires - 56vac
(2)Green wires - 7.68vac
(2)Red wires - 633vac....(woohoo)
(1)Green/yellow wire that was attached to chassis......didnt measure that at all.......not sure exactly what it does(center tap of some sort maybe???).
So yeah....no amperage readings, but I was apparently wrong about not having any filament power. Its been a few years since I got the unit.....I must of been thinking of another "project"......
anyway here is a pic of the carnage......
An externally hosted image should be here but it was not working when we last tested it.
Obviously I was testing the cloth cover wires......
so what is the best way to get amperage specs on a tranformer such as this?
Thanks again.....
Nate
Nate,
Use the Knight O/P trafo in a Mullard style circuit. A 6AB4 voltage amplifier and a 6J6 LTP splitter/driver will yield plenty of gain. An AnTek AN-4T360 power trafo will provide all you need. SS rectify the B+. Voltage multiply 1 of the paired 5 A./6.3 VAC windings to obtain the negative bias rail. The 2nd filament winding has current to spare for the 4 signal tubes.
If the Knight O/P trafo lacks UL taps, Maida Regulate g2 B+.
Use the Knight O/P trafo in a Mullard style circuit. A 6AB4 voltage amplifier and a 6J6 LTP splitter/driver will yield plenty of gain. An AnTek AN-4T360 power trafo will provide all you need. SS rectify the B+. Voltage multiply 1 of the paired 5 A./6.3 VAC windings to obtain the negative bias rail. The 2nd filament winding has current to spare for the 4 signal tubes.
If the Knight O/P trafo lacks UL taps, Maida Regulate g2 B+.
Eli,
I really do appreciate the help and all the info, but I really wasnt kidding when I said I was cheap(I ain't broke.....but I'm badly bent....lol).
Ive got a long sad story(bad back....no work).....not to mention a wedding(that we're paying for ourselves) coming up, so seriously; I'm trying to do this project with parts on hand, or MAYBE a $20(shipped) ebay transformer.
Granted, the transformer you suggested is only $50, by the time you add shipping.....its just not in the budget.
Thanks again though....I'll use what info of yours I can.....
Nate
I really do appreciate the help and all the info, but I really wasnt kidding when I said I was cheap(I ain't broke.....but I'm badly bent....lol).
Ive got a long sad story(bad back....no work).....not to mention a wedding(that we're paying for ourselves) coming up, so seriously; I'm trying to do this project with parts on hand, or MAYBE a $20(shipped) ebay transformer.
Granted, the transformer you suggested is only $50, by the time you add shipping.....its just not in the budget.
Thanks again though....I'll use what info of yours I can.....
Nate
Nate,
Insufficient coin of the realm bedevils us throughout life.
Time for "Plan B".
You have mail! Build a 1 channel "El Cheapo" variant on the Thomas chassis. Contact Jim McShane, to obtain the EL84/6BQ5 cathode bias network values. Get the additional power "iron" from Aliied Electronics. $12.41 buys the B- trafo and $7.74 buys a Triad C-24X filter choke. SS rectify the B+, as you need the Volts and UF4007s cost about 15 cents each.
Insufficient coin of the realm bedevils us throughout life.
Time for "Plan B".You have mail! Build a 1 channel "El Cheapo" variant on the Thomas chassis. Contact Jim McShane, to obtain the EL84/6BQ5 cathode bias network values. Get the additional power "iron" from Aliied Electronics. $12.41 buys the B- trafo and $7.74 buys a Triad C-24X filter choke. SS rectify the B+, as you need the Volts and UF4007s cost about 15 cents each.
Re: took some basic measurements
So, what's wrong with using this guy as your power transformer? If the only hangup is not knowing the current limits, you might be able to guess by looking at what it used to drive. I've also found this article to be extremely helpful:
http://www.diytube.com/phpBB2/viewtopic.php?t=1465&start=7
camusmuse said:
So, what's wrong with using this guy as your power transformer? If the only hangup is not knowing the current limits, you might be able to guess by looking at what it used to drive. I've also found this article to be extremely helpful:
http://www.diytube.com/phpBB2/viewtopic.php?t=1465&start=7
Eli.
Yeah......I think im pretty much sold on El Cheapo.....
I found the "bargain basement" thread on another forum....got to page six, then decided to skip to the end to make sure it was still alive.....I WILL read the whole thing though.......pretty fascinating, and very encouraging too.....great stuff.
Whats the best way of "getting a hold of" Mr. McShane?
Is the ElCheapo "bridgable"? It would be nice to be able to make a "real one", or at least have the extra power...if just for the "head room".
When you suggest that I use the Thomas chassis, do you mean use the output trans as well, or do I need the specific one that the amp was designed for. FWIW, I am actually going to custom build a chassis for the amp anyway. But I do plan on reusing the sockets and anything else I can.....which brings me to the next question....
Are there still "kits" available? If so from whom?
Thanks again.......
Nate
Yeah......I think im pretty much sold on El Cheapo.....
I found the "bargain basement" thread on another forum....got to page six, then decided to skip to the end to make sure it was still alive.....I WILL read the whole thing though.......pretty fascinating, and very encouraging too.....great stuff.
Whats the best way of "getting a hold of" Mr. McShane?
Is the ElCheapo "bridgable"? It would be nice to be able to make a "real one", or at least have the extra power...if just for the "head room".
When you suggest that I use the Thomas chassis, do you mean use the output trans as well, or do I need the specific one that the amp was designed for. FWIW, I am actually going to custom build a chassis for the amp anyway. But I do plan on reusing the sockets and anything else I can.....which brings me to the next question....
Are there still "kits" available? If so from whom?
Thanks again.......
Nate
Nate,
Jim McShane's web site is here. AFAIK, Jim still has small parts kits for "El Cheapo".
For a mono amp, recycle the power and O/P trafos on the Thomas chassis. If the Thomas O/P trafo has UL taps, use 'em and get an honest 12 W. "El Cheapo" works well with mediocre O/P "iron", but better stuff, like DynaClone Z565s, is taken advantage of.
Bridging tubed power amps can be problematic. You have to connect 16 Ohm speakers to the 8 Ohm taps and 8 Ohm speakers to the 4 Ohm taps. Unless the O/P trafos are most unusual, 4 Ohm speakers are out, when bridged mode is employed.
Jim McShane's web site is here. AFAIK, Jim still has small parts kits for "El Cheapo".
For a mono amp, recycle the power and O/P trafos on the Thomas chassis. If the Thomas O/P trafo has UL taps, use 'em and get an honest 12 W. "El Cheapo" works well with mediocre O/P "iron", but better stuff, like DynaClone Z565s, is taken advantage of.
Bridging tubed power amps can be problematic. You have to connect 16 Ohm speakers to the 8 Ohm taps and 8 Ohm speakers to the 4 Ohm taps. Unless the O/P trafos are most unusual, 4 Ohm speakers are out, when bridged mode is employed.
I was thinking more of "bridging" before the output trans, kinda like "stacking" the tubes(not sure if that is the correct way to describe it. or if it is even possible with the elcheapo design). The output trans that is on the thomas is pretty small, so I was considering using the output trans from the knight, as it was used with a pp el34 setup, which from what I understand is very similar to the dynaclones(or at least the original dynacos.
I use to have two st-70s that were each run in mono.......boy I miss them....lol. They were running a pair of basically stock Infinity Quantum 5s which surely ran lower than 4 ohms at times....the dynacos never seemed to mind too much......
Thanks again for your time....
Nate
I use to have two st-70s that were each run in mono.......boy I miss them....lol. They were running a pair of basically stock Infinity Quantum 5s which surely ran lower than 4 ohms at times....the dynacos never seemed to mind too much......
Thanks again for your time....
Nate
Nate,
I think what you have in mind is parallel-push-pull (PPP). 4X EL84s set up PPP will work just fine with an EL34 O/P trafo. However, the ride (as is always the case) is not free. Several considerations dictate that you use "fixed" bias and an individual bias trim pot. for each "final". DC blocking considerations force the use of an individual coupling cap. to each EL84 grid. Last, but definitely not least, is the power trafo. A trafo capable of feeding a PP pair of EL84s will "fry" trying to feed a PPP quad.
I think what you have in mind is parallel-push-pull (PPP). 4X EL84s set up PPP will work just fine with an EL34 O/P trafo. However, the ride (as is always the case) is not free. Several considerations dictate that you use "fixed" bias and an individual bias trim pot. for each "final". DC blocking considerations force the use of an individual coupling cap. to each EL84 grid. Last, but definitely not least, is the power trafo. A trafo capable of feeding a PP pair of EL84s will "fry" trying to feed a PPP quad.
I had a feeling that would be the case(my "el84" trans not being up to snuff), and kinda puts me back to square one.......probably will do the regular "single channel variant" for my current project....
Still havent contated Mr. McShane, as my wallet is literally empty at the moment, I will as soon as finance and fiance permits......slight pun intended...however she is VERY tolerant of my "addiction"
However, even if I dont have the proper ps now, I would be interested in this "PPP" mono version if you wanted to put some time into it.....im still reading the bargain basement post....as is seems to be a good record of the development of the el cheapo. I would like to use this more for a learning experience than just "getting another amp". Always wanted to learn that "black magic" of tube design.....
I really would like to do a "mono ppp el cheapo"...... for my "real" system, I'm an avid JBL fan....just need to build some cabinets and bend some acrylic(I have literally a ton of the stuff in 1/4 inch.......gonna build(bend) some horn lenses outta them, and maybe some boxes.....once I decide how to laminate the sheets......design "still in the works". I'm more of a speaker builder than anything......was a "pro" at one point in my life......
Sold the before mentioned dynacos that were originally gonna power the "real" system.... to buy a van......that was quickly totaled in a "not my fault crash"....that also totaled my back and career with the IATSE......5 herniated discs and counting.....cest la vie.......at least im still alive.
anyway enough of my sad story......if you are interested in the ppp......just say the word...ill do whatever i can to help.......what i have planned will need at least six of "those"....(i reallly like active crossovers) It will be borderline PA.......but im also half deaf....go figure......lol......ironically too many ear infections as a child.......and a stint as a car stereo nut in high school....mid 90's.....when americans made REAL amps......
thanks again Eli......you are a wealth of information here......I hope our conversations can continue.....
Nate
Still havent contated Mr. McShane, as my wallet is literally empty at the moment, I will as soon as finance and fiance permits......slight pun intended...however she is VERY tolerant of my "addiction"
However, even if I dont have the proper ps now, I would be interested in this "PPP" mono version if you wanted to put some time into it.....im still reading the bargain basement post....as is seems to be a good record of the development of the el cheapo. I would like to use this more for a learning experience than just "getting another amp". Always wanted to learn that "black magic" of tube design.....
I really would like to do a "mono ppp el cheapo"...... for my "real" system, I'm an avid JBL fan....just need to build some cabinets and bend some acrylic(I have literally a ton of the stuff in 1/4 inch.......gonna build(bend) some horn lenses outta them, and maybe some boxes.....once I decide how to laminate the sheets......design "still in the works". I'm more of a speaker builder than anything......was a "pro" at one point in my life......
Sold the before mentioned dynacos that were originally gonna power the "real" system.... to buy a van......that was quickly totaled in a "not my fault crash"....that also totaled my back and career with the IATSE......5 herniated discs and counting.....cest la vie.......at least im still alive.
anyway enough of my sad story......if you are interested in the ppp......just say the word...ill do whatever i can to help.......what i have planned will need at least six of "those"....(i reallly like active crossovers) It will be borderline PA.......but im also half deaf....go figure......lol......ironically too many ear infections as a child.......and a stint as a car stereo nut in high school....mid 90's.....when americans made REAL amps......
thanks again Eli......you are a wealth of information here......I hope our conversations can continue.....
Nate
Nate,
Does the EL34 O/P trafo have ultralinear (UL) taps? If not, let's stop. Full pentode mode requires a regulated g2 B+ supply and nested NFB loops.
OTOH, if the O/P trafo does have UL taps, a monoblock "El Cheapo" variant using PPP "finals" is quite feasible. If the O/P trafo is suitable, register at AudiophileTalk and we'll continue in the Bargain Basement thread. It's a matter of consolidation.
Does the EL34 O/P trafo have ultralinear (UL) taps? If not, let's stop. Full pentode mode requires a regulated g2 B+ supply and nested NFB loops.
OTOH, if the O/P trafo does have UL taps, a monoblock "El Cheapo" variant using PPP "finals" is quite feasible. If the O/P trafo is suitable, register at AudiophileTalk and we'll continue in the Bargain Basement thread. It's a matter of consolidation.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.