So, I'm almost done with a PCB based build of my flea amplifier, and will be stripping the original p2p prototype and building my first personal SE amplifier in years. On the original chassis I have a 50VA power transformer, a mosfet ripple filter that gives about 290 volts under load, and four octal sockets, input RCAs, and speaker binding posts that will stay in the chassis. I will be using 6V6GT( Russian 6P6, actually) and a pair of surplus fender champ style output transformer for my outputs, which will leave me with two octal sockets for input circuitry. Planing on going for tetrode, and maybe triode connected, if the drivers can handle it. I would like to use global negative feedback.
So far I've toyed with two ideas for it. Either a CCDA front end with 6SL7 feeding a 6SN7 cathode follower, or a 6SL7 totem pole. No desire to go SRPP, unless there is a compelling reason to.
I suppose I could make some adapter discs to convert to nine pin input tubes if needed, and then could also use 6N1P, or 6N2P, or similar tubes, limited to what I have on hand.
What would you do?
So far I've toyed with two ideas for it. Either a CCDA front end with 6SL7 feeding a 6SN7 cathode follower, or a 6SL7 totem pole. No desire to go SRPP, unless there is a compelling reason to.
I suppose I could make some adapter discs to convert to nine pin input tubes if needed, and then could also use 6N1P, or 6N2P, or similar tubes, limited to what I have on hand.
What would you do?
I usually leave it hooked to the TV, so something from 1V peak for full output would be good and versatile enough for most of what I'm likely to do with it, as that's what the current flea ampl is at and it does well. It'll either be there or used with a tablet or phone that will do 300mV RMS in the garage, for background workshop tunes.
I'm leaning towards more gain so that I can have enough headroom to play with for feedback, and a 6SL7 totem pole should give me around 30~35x which should be usable for tetrode, but maybe not triode. If I go triode (might as well with the 6V6, it really is a fine triode, if not the most powerful) I'd rather have a bit more gain.
I'm thinking that the 6SL7 into 6SN7 would be best, that way I can go for the bypassed cathode up front and a cathode follower for oomph driving the triode connected grid capacitance. Direct coupled to the preceding anode should still be plenty of headroom for swing.
I'm leaning towards more gain so that I can have enough headroom to play with for feedback, and a 6SL7 totem pole should give me around 30~35x which should be usable for tetrode, but maybe not triode. If I go triode (might as well with the 6V6, it really is a fine triode, if not the most powerful) I'd rather have a bit more gain.
I'm thinking that the 6SL7 into 6SN7 would be best, that way I can go for the bypassed cathode up front and a cathode follower for oomph driving the triode connected grid capacitance. Direct coupled to the preceding anode should still be plenty of headroom for swing.
You could go "old school" and use 6SJ7 input 
http://www.mif.pg.gda.pl/homepages/frank/sheets/049/6/6SJ7.pdf
Found this on a Korean forum...
http://www.mif.pg.gda.pl/homepages/frank/sheets/049/6/6SJ7.pdf
Found this on a Korean forum...
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Would if I had a pair this is a "sweep the floor" rebuild that will be limited to parts that I've already got on hand.
I'm thinking a totem pole might be a good way to go. Maybe bite the bullet and try an SRPP just for the hell of it? At modest swing like I'm going to need, and with some global negative feedback I think it would be plenty good. If I'm not mistaken kevinkr did a 6SL7 SRPP into 45 SE a few years back and had good things to say about it. Triode connected 6V6 is (allegedly) very close to 45, so might be worth a shot?
Anybody done totem pole with bypassed cathode resistor on the bottom tube? Gain should be close to mu that way unless there's something I'm missing.
this is a "sweep the floor" rebuild that will be limited to parts that I've already got on hand.I'm thinking a totem pole might be a good way to go. Maybe bite the bullet and try an SRPP just for the hell of it? At modest swing like I'm going to need, and with some global negative feedback I think it would be plenty good. If I'm not mistaken kevinkr did a 6SL7 SRPP into 45 SE a few years back and had good things to say about it. Triode connected 6V6 is (allegedly) very close to 45, so might be worth a shot?
Anybody done totem pole with bypassed cathode resistor on the bottom tube? Gain should be close to mu that way unless there's something I'm missing.
^ If I had a pair of 6SH7 or 6SJ7 I would try something like that Financially I'm not in a position to sink any additional money into my hobbies for a while, but I happen to have quite a bit of parts on hand, other than higher quality iron.
Maybe a 6SN7 beta follower, like Morgan Jones featured in his Designing Valve Amplifiers books? Should be an interesting solution that would be something different. A 6SN7 in this configuration shouldn't have an issue driving a triode connected 6V6 in this setup, and overall distortion should be low without negative feedback. A pair of cheap Russian 6H8C/6SN7 should be fine here, and I have a dozen or so on hand.
Just found the cheap transformers that I had on hand, and they're 7.5k to 8/4/16 ohm. They are for the Epiphone valve junior, and are rated at 5W with a 6V6. I doubt they have bandwidth past 10khz, but they'll do for a quick garage amp rebuild like this. Might be able to extend the bandwidth with some feedback, but without a way to test it there's not much point.
This thing is for background tunes while sawing wood, beating on seized bolts, etc. When we end up in a place with room for bigger, better speakers out in the shop I'll build a bigger rig with nice parts.
Financially I'm not in a position to sink any additional money into my hobbies for a while, but I happen to have quite a bit of parts on hand, other than higher quality iron.Maybe a 6SN7 beta follower, like Morgan Jones featured in his Designing Valve Amplifiers books? Should be an interesting solution that would be something different. A 6SN7 in this configuration shouldn't have an issue driving a triode connected 6V6 in this setup, and overall distortion should be low without negative feedback. A pair of cheap Russian 6H8C/6SN7 should be fine here, and I have a dozen or so on hand.
Just found the cheap transformers that I had on hand, and they're 7.5k to 8/4/16 ohm. They are for the Epiphone valve junior, and are rated at 5W with a 6V6. I doubt they have bandwidth past 10khz, but they'll do for a quick garage amp rebuild like this. Might be able to extend the bandwidth with some feedback, but without a way to test it there's not much point.
This thing is for background tunes while sawing wood, beating on seized bolts, etc. When we end up in a place with room for bigger, better speakers out in the shop I'll build a bigger rig with nice parts.
Two triode stages in cascode act like a pentode in a lot of ways. Merlin's page is pretty helpful:
The Valve Wizard
The schematic I posted was discussed in another thread briefly. The accompanying article is an interesting read, and the whole purpose of the circuit was to utilize budget OTs, sort of like what you are doing. Here is a post with the article:
https://www.diyaudio.com/forums/tubes-valves/340415-local-feedback-grid-cathode-3.html#post5858194
The images may be hard to read, so here is a link to a pdf:
https://www.americanradiohistory.com/Archive-Audio/50s/Audio-1955-Mar.pdf
The Valve Wizard
The schematic I posted was discussed in another thread briefly. The accompanying article is an interesting read, and the whole purpose of the circuit was to utilize budget OTs, sort of like what you are doing. Here is a post with the article:
https://www.diyaudio.com/forums/tubes-valves/340415-local-feedback-grid-cathode-3.html#post5858194
The images may be hard to read, so here is a link to a pdf:
https://www.americanradiohistory.com/Archive-Audio/50s/Audio-1955-Mar.pdf
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Emergency/backup cash yes, but not that I can really use in good conscience for the next month until I get some more overtime on the next few checks. I got two flat tires in the span of a week, and missed a day of work and am playing catch-up for now.
I could easily slap together a bunch of solid state stuff with what's on hand (I have everything to make up four LM3886 amps) but I wanted to repurpose this chassis for a cute piece of gear for the garage
If I had the cash for more transformers I would be finishing the 12AV5GA build I've been planning, rather than an SE amp
I could easily slap together a bunch of solid state stuff with what's on hand (I have everything to make up four LM3886 amps) but I wanted to repurpose this chassis for a cute piece of gear for the garage
If I had the cash for more transformers I would be finishing the 12AV5GA build I've been planning, rather than an SE amp
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