Hi,
for my next project, ... i want to build a higher power push pull amp.
I have snagged off ebay,a scavenged power/ OPT pair for the fisher 800c (electrically almost idential to the popular 500c reciever). this piece had a push pull 7591 amp. therefore, my choice of amp is dependant on this set.
i hope the trannies etc are not shorted etc . i should be getting the items next week.
i wish to
the transformers were originally meant to be used with 7591 output tubes.
q. these tubes have recently been re-introduced into the market. how are they, compared to the hard to find NOS tubes (i read opinions on the internet saying the replacements are basically 6L6 tubes)
q. apart from 7591, are there any other output tubes i could use in this circuit (sorry, i don't have the tranny numbers with me although a 500c schematic can be found at http://www.fortunecity.com/tinpan/beegee/290/page4.html ).
thanks
for my next project, ... i want to build a higher power push pull amp.
I have snagged off ebay,a scavenged power/ OPT pair for the fisher 800c (electrically almost idential to the popular 500c reciever). this piece had a push pull 7591 amp. therefore, my choice of amp is dependant on this set.
i hope the trannies etc are not shorted etc . i should be getting the items next week.
i wish to
the transformers were originally meant to be used with 7591 output tubes.
q. these tubes have recently been re-introduced into the market. how are they, compared to the hard to find NOS tubes (i read opinions on the internet saying the replacements are basically 6L6 tubes)
q. apart from 7591, are there any other output tubes i could use in this circuit (sorry, i don't have the tranny numbers with me although a 500c schematic can be found at http://www.fortunecity.com/tinpan/beegee/290/page4.html ).
thanks
zobsky said:
No, the Sovtek 7591 tubes are real 7591 tubes. The 7591XYZ tubes they used to make were re-based 6L6s.
If you mean with these transformers then yes - 6L6, EL34, 6B4G and many others. If you're talking about the exact same circuit as the 500C, you can only use the 7591, 7868 or the 6GM5. You can change the circuit to suit other tubes though.
Best regards,
Mikkel C. Simonsen
Re: Re: next project: rebuild using fisher 500c trannies
At this point, the only component that is fixed are the output tranny combination, ..
i'd like to reuse the same power transformer but if i can build a better amp using an (output compatible) tube which needs a different voltage, i can get another power tranny with not too much trouble.
opinions, ... recommendations, ... attributes of different tube combinations, circuit topologies .... <fill in here>
speaker efficiency is not an issue here, since i have a bunch of various types at home,.. more so is the best possible sound i can get using tubes compatible with the available output transfomers (at a real-world cost).
thanks very much, .. keep the replies coming.
thanks for the info, ...mcs said:
At this point, the only component that is fixed are the output tranny combination, ..
i'd like to reuse the same power transformer but if i can build a better amp using an (output compatible) tube which needs a different voltage, i can get another power tranny with not too much trouble.
opinions, ... recommendations, ... attributes of different tube combinations, circuit topologies .... <fill in here>
speaker efficiency is not an issue here, since i have a bunch of various types at home,.. more so is the best possible sound i can get using tubes compatible with the available output transfomers (at a real-world cost).
thanks very much, .. keep the replies coming.
If you want to use nice old NOS tubes, try an 807. They are available DIRT CHEAP and have a similar plate dissipation and specs to a 6L6GC. They are also quite beautiful with their ST shape and topcap. They sound great in UL or pentode (not so good in triode IMHO.)
I recently bought a quad of NOS 807s for US$20, another quad was given to me! Try buying a NOS quad of EL34s or 6L6GC for that sort of price!
I used the schematic found at http://hollowstate.netfirms.com/DIY_files/proto.htm
except with an Em81 magic eye and cathode biased output tubes in UL... Also only about 250V on the 6SN7s. Sounds great!
I recently bought a quad of NOS 807s for US$20, another quad was given to me! Try buying a NOS quad of EL34s or 6L6GC for that sort of price!
I used the schematic found at http://hollowstate.netfirms.com/DIY_files/proto.htm
except with an Em81 magic eye and cathode biased output tubes in UL... Also only about 250V on the 6SN7s. Sounds great!
Hi
the trannies should be here by the end of next week.
narrowing down the design goals a bit
1. choice of tubes:7591 or 807 , .. the 807s are about 3-4 times cheaper than 7591 tubes. they certainly look cooler, ... i see a lot of varying opinions on 807 tube amps on the www, .. but could this be more due to circuit implementation rather than the tube itself?
any other good tubes i could use?
2. circuit choice, .. i guess i could try almost any of the stuff in the push pull section of the fi-primer. ...but can anyone suggest an even better tried & proven circuit?
thanks
the trannies should be here by the end of next week.
narrowing down the design goals a bit
1. choice of tubes:7591 or 807 , .. the 807s are about 3-4 times cheaper than 7591 tubes. they certainly look cooler, ... i see a lot of varying opinions on 807 tube amps on the www, .. but could this be more due to circuit implementation rather than the tube itself?
any other good tubes i could use?
2. circuit choice, .. i guess i could try almost any of the stuff in the push pull section of the fi-primer. ...but can anyone suggest an even better tried & proven circuit?
thanks
zobsky said:
The 807 and 7591 are VERY different tubes, so don't expect them to sound the same
But both tubes are good, so use whatever you want...
How about a Williamosn? Even better - who knows? But certainly tried and proven - have a look here: http://stiftsbogtrykkeriet.dk/~mcs/ (at the bottom of the page).
Best regards,
Mikkel C. Simonsen
The Fisher OPT's are a 6k6 design of reasonable but not great quality. I own an 800B and have "borrowed" the OPTs to try in other projects. The Fisher uses a voltage doubler in the power supply so the trans has quite a low voltage. The schematic is not to hand, but it's about 150-170V. Personally I'd ditch it and use a FW with 12AX4GT's/6CJ3's, but that's just my preference.
Depending on how you want to run the output tubes (triode or pentode) and the amount of power you want from them, there are a ton of options from 2A3/6B4G to 7591/EL34 pentode amongst others.
The 800B's are supposedly rated for about 37W/ch, and the max continuous current recommended was 60mA-ish for the OPT's (thinking class A triode). There are no UL taps on the primary, but I've never heard a really great UL amp yet.
Shifty's 807 idea is good. they're great tubes and cheap, but running them high voltage (~400) in triode sounds crap but gives max power. 300V/70mA per tube works better sonically but is low power, and in pentode, the STC datasheet from the Retrovox site gives excellent starting points, esp if you study the distortion curves.
The new 7591 is a good tube. Mine haven't given any problems in service and sound fine in the original circuit. I've not tried them much elsewhere, or trioded in the Fisher, as the Fisher is a nice lush sounding but only modest resolution design.
If you don't need a lot of power, I'd go with the 2A3 stigla/RPower PP design. Do a search here to find details.
Depending on how you want to run the output tubes (triode or pentode) and the amount of power you want from them, there are a ton of options from 2A3/6B4G to 7591/EL34 pentode amongst others.
The 800B's are supposedly rated for about 37W/ch, and the max continuous current recommended was 60mA-ish for the OPT's (thinking class A triode). There are no UL taps on the primary, but I've never heard a really great UL amp yet.
Shifty's 807 idea is good. they're great tubes and cheap, but running them high voltage (~400) in triode sounds crap but gives max power. 300V/70mA per tube works better sonically but is low power, and in pentode, the STC datasheet from the Retrovox site gives excellent starting points, esp if you study the distortion curves.
The new 7591 is a good tube. Mine haven't given any problems in service and sound fine in the original circuit. I've not tried them much elsewhere, or trioded in the Fisher, as the Fisher is a nice lush sounding but only modest resolution design.
If you don't need a lot of power, I'd go with the 2A3 stigla/RPower PP design. Do a search here to find details.
update, i've beenreading up a bit.
1. i recieved the power / output transformers this week. Brett's suggestion to chuck the power tranny is wise
2. the next question is which circuit to use. Mikkel suggests williamson / mod williamson. my vintage 6v6 pilot amps are williamson, but i can't bear to modify them. i guess i could build a williamson but i was looking for something more exotic, ... the idea of using interstage transformer as a phase splitter in the ralph PP appeals to me. in this regard:
a. how expensive are lundahl ITs, .. couldn't get an idea off their web page but i'm estimating $150 or so per pair. i have seen references to ha
b. are their any cheaper alternatives which perform as well? I have seen http://diyparadise.com/pt156.html but would like to hear from someone who may have tried this.
c. would using this kind of topology with my fisher transformers be like putting skinny tires on a sports car ie. bottleneck being the fishers?
d. parafeed vs. regular IT, .. can someone give me the lowdown. From my readings, parafeed makes things a bit more economical by ensuring that the IT doesn't have to deal with DC (courtesy of the DC blocking cap) but in doing so,it complicates matters in that we introduces an additional component in the signal path, as opposed to conventional IT coupling
e. kind of a naive question, ..but does conventional IT coupling have the same benefits as plate choke loading, as the feed from the plate passes through the primary of the IT?
2. still not sure which path to follow as far as tubes to use.
a. 7591 tubes are about $75 a quad (new sovtek) and will give me more power
b. Brett, what is "FW" as in "Personally I'd ditch it and use a FW with ...."
c. still considering the 807 vs. the 2a3/6b4g. something like $50 for a quad vs. $150 for a quad for the 2a3. as far as tube flavours, my listening experience in tubes so far has been limited to 6bq5 (SE, pentode / triode), 6v6 (push pull), DHT 2a3 (SE - bottlehead paramor). Brett, you suggest 807 in pentode, as opposed to tride at lower voltages. what is the opinion based on (distortion curves or just the sound signature .
d. the fi primer also suggests a DC coupled 6ck4 indirectly heated triode (http://tinpan.fortunecity.com/saints/668/primer/pp.html , http://tinpan.fortunecity.com/saints/668/primer/6ck4-pp.gif). any opinions about this, .. seems like another elegant design., tubes should run about $45 for a quad.
3. another interesting link i came across describes a rebuild and extensive mods using the same fisher 500c transformers in a IT / parafeed PP arrangement. this project uses type 47 tubes (i have hardly been able to find any sources for this tube on the www) at http://home.pacifier.com/~gpimm/47.htm .) if you notice , he uses an IT as a phase splitter and feeds the output to the driver tubes (the reverse of most schematics). opinions?
1. i recieved the power / output transformers this week. Brett's suggestion to chuck the power tranny is wise
2. the next question is which circuit to use. Mikkel suggests williamson / mod williamson. my vintage 6v6 pilot amps are williamson, but i can't bear to modify them. i guess i could build a williamson but i was looking for something more exotic, ... the idea of using interstage transformer as a phase splitter in the ralph PP appeals to me. in this regard:
a. how expensive are lundahl ITs, .. couldn't get an idea off their web page but i'm estimating $150 or so per pair. i have seen references to ha
b. are their any cheaper alternatives which perform as well? I have seen http://diyparadise.com/pt156.html but would like to hear from someone who may have tried this.
c. would using this kind of topology with my fisher transformers be like putting skinny tires on a sports car ie. bottleneck being the fishers?
d. parafeed vs. regular IT, .. can someone give me the lowdown. From my readings, parafeed makes things a bit more economical by ensuring that the IT doesn't have to deal with DC (courtesy of the DC blocking cap) but in doing so,it complicates matters in that we introduces an additional component in the signal path, as opposed to conventional IT coupling
e. kind of a naive question, ..but does conventional IT coupling have the same benefits as plate choke loading, as the feed from the plate passes through the primary of the IT?
2. still not sure which path to follow as far as tubes to use.
a. 7591 tubes are about $75 a quad (new sovtek) and will give me more power
b. Brett, what is "FW" as in "Personally I'd ditch it and use a FW with ...."
c. still considering the 807 vs. the 2a3/6b4g. something like $50 for a quad vs. $150 for a quad for the 2a3. as far as tube flavours, my listening experience in tubes so far has been limited to 6bq5 (SE, pentode / triode), 6v6 (push pull), DHT 2a3 (SE - bottlehead paramor). Brett, you suggest 807 in pentode, as opposed to tride at lower voltages. what is the opinion based on (distortion curves or just the sound signature .
d. the fi primer also suggests a DC coupled 6ck4 indirectly heated triode (http://tinpan.fortunecity.com/saints/668/primer/pp.html , http://tinpan.fortunecity.com/saints/668/primer/6ck4-pp.gif). any opinions about this, .. seems like another elegant design., tubes should run about $45 for a quad.
3. another interesting link i came across describes a rebuild and extensive mods using the same fisher 500c transformers in a IT / parafeed PP arrangement. this project uses type 47 tubes (i have hardly been able to find any sources for this tube on the www) at http://home.pacifier.com/~gpimm/47.htm .) if you notice , he uses an IT as a phase splitter and feeds the output to the driver tubes (the reverse of most schematics). opinions?
With a 6.6K p-p primary. the EL34 is an obvious choice. EL37 would be even better, but good luck finding those. I'm experimenting at the moment with some 6BG6s that I picked up on the cheap. These versions seem to be pretty much identical to the fabulous 7027As, other than the pin-out.
Want an exotic input circuit? Here's what I'm using at the moment in my Eico HF87 (also with 6.6K o/p trannies). Input transformers are, IMO, a better choice than interstage. You can get fancier with the current source, but I haven't gone in and measured the effect yet; the simple one seems to work and sound fine. The feedback is taken from the 16 and zero ohm secondary taps, with the 4 ohm tap being grounded. As you can tell, I like balance!
Want an exotic input circuit? Here's what I'm using at the moment in my Eico HF87 (also with 6.6K o/p trannies). Input transformers are, IMO, a better choice than interstage. You can get fancier with the current source, but I haven't gone in and measured the effect yet; the simple one seems to work and sound fine. The feedback is taken from the 16 and zero ohm secondary taps, with the 4 ohm tap being grounded. As you can tell, I like balance!
Attachments
The 6BG6 project is still a work-in-process, in the proto stage I demonstrated in the "Ugly Prototypes Contest" thread. I'm actually using EL37s in the Eico right now for listening; I think they're fantastic for this app, but they're my last set and finding/paying for replacements is well past my margin of pain. That's why getting the 6BG6s to work in this application is a high priority When I'm done (I still have to check it out with some 4300 ohm trannies), I'll post the results. These tubes are really cheap, but might turn out to be something really special.
When I'm done (I still have to check it out with some 4300 ohm trannies), I'll post the results. These tubes are really cheap, but might turn out to be something really special.
Hi,
Once had a couple of Westrex monoblocks using 6BG6s.
It's a very tough tube, virtually indestructable, sounded good too.
The Westrexs' sounded a little dated, rather darkish, but still had good bass.
It's hard to tell tell much of the qualities are due to the tube itself but it certainly is well worth investigating.
Cheers,
Once had a couple of Westrex monoblocks using 6BG6s.
It's a very tough tube, virtually indestructable, sounded good too.
The Westrexs' sounded a little dated, rather darkish, but still had good bass.
It's hard to tell tell much of the qualities are due to the tube itself but it certainly is well worth investigating.
Cheers,
according to some info on the web ( eg http://groups.google.com/groups?q=6...UTF-8&selm=5j38va$quv@news1.mnsinc.com&rnum=9 ), the 6bg6 and the 807 are near equivalents except for the base and also be used in 6l6 based designs.
It depends on the 6BG6. Some of the ones I have on hand do indeed look like 807s, albeit with smaller plate structures (20W Pd). The ones I'm checking out now are claimed to be rebased 7027/7581 types (30w Pd), and sure look that way. I'll take some comparative photos later and post them. BTW, they listed as NOS at $6 a pop.
i think i'll take a chance on the 6BG6 (a little more power than the 807) since there is not much to lose even if they don't turn out well. they should work with the fisher trannies. i'll postpone my DHT 2A3 push pull plans till after I have had a chance to see how these things work (plan to order tomorrow). I'll document the build in this thread. If things go well, I should be able to build this amp for $150 to $200 (if I don't use exotic IT iron) which should be an amazing value if it sounds good.
may look at the 807 schematics mentioned in this thread
everyone on this thread has suggested to stay away from triode operation on the 807, .. and i assume the same for the 6bG6 too??, .. but why??? , .. a matter of sound ??
so far,
topology: push pull
circuit: to be decided
output iron: fisher 500C / 800C
tubes: 6bG6
input iron: to be scrounged depending on the circuit to use.
driver tubes: to be decided
i'll search around on the www and maybe look at the tube curves and post back when i have new info.
thanks,
may look at the 807 schematics mentioned in this thread
everyone on this thread has suggested to stay away from triode operation on the 807, .. and i assume the same for the 6bG6 too??, .. but why??? , .. a matter of sound ??
so far,
topology: push pull
circuit: to be decided
output iron: fisher 500C / 800C
tubes: 6bG6
input iron: to be scrounged depending on the circuit to use.
driver tubes: to be decided
i'll search around on the www and maybe look at the tube curves and post back when i have new info.
thanks,
zobsky said:
Been away again and have just seen your post. Lundahl prices in the US can be found here.
http://hometown.aol.com/kevinc927/myhomepage/business1.html
I beleive the 1660 are the best for this application, but email Kevin and ask. Very knowledgable and helpful.
thanks for the pricing info on lundahl ITs,
as i progress towards defining the components in this project, ...
i want to question / understand the differences and expected advantages / disadvantages in expected performance / sound between an IT vs coupling cap, ..but wanted to read up a little more before i can construct intelligent questions on this topic.
oops, too late, i already asked
as i progress towards defining the components in this project, ...
i want to question / understand the differences and expected advantages / disadvantages in expected performance / sound between an IT vs coupling cap, ..but wanted to read up a little more before i can construct intelligent questions on this topic.
oops, too late, i already asked
BTW, .... wondering about these line matching transformers (ridiculously low price)
http://www.edcorusa.com/magnetics/audio/wsm/wsm10k-10k.htm
mentioned here
http://boozhoundlabs.com/edcor/
would they work? perhaps, but how well? if not as an IT, it might be possible to use it as a phase splitter on the input itself.
also, why might input stage iron be a better choice than IT iron (SY) ?
http://www.edcorusa.com/magnetics/audio/wsm/wsm10k-10k.htm
mentioned here
http://boozhoundlabs.com/edcor/
would they work? perhaps, but how well? if not as an IT, it might be possible to use it as a phase splitter on the input itself.
also, why might input stage iron be a better choice than IT iron (SY) ?
Why input xfrmers?
I prefer keeping voltage swings and currents through the iron as low as possible. So, 1V (more or less) is more appealing than 50V (more or less).
And a well-chosen input transformer gives you really good common-mode noise rejection. I'm using the Jensen JT-11-P1 (thanks to Steve Eddy for talking me into trying them), and it works as advertised, does a fine job producing a balanced signal, has good bandwidth and very low distortion, and is relatively inexpensive. So doing it this way kills two birds with one stone. The disadvantage is that it works best with a 10K load, which is a bit low for most tube preamps to drive. OTOH, Jensen claims that an RC snubber will allow higher load resistances; haven't tried that yet, but it makes sense.
I prefer keeping voltage swings and currents through the iron as low as possible. So, 1V (more or less) is more appealing than 50V (more or less).
And a well-chosen input transformer gives you really good common-mode noise rejection. I'm using the Jensen JT-11-P1 (thanks to Steve Eddy for talking me into trying them), and it works as advertised, does a fine job producing a balanced signal, has good bandwidth and very low distortion, and is relatively inexpensive. So doing it this way kills two birds with one stone. The disadvantage is that it works best with a 10K load, which is a bit low for most tube preamps to drive. OTOH, Jensen claims that an RC snubber will allow higher load resistances; haven't tried that yet, but it makes sense.
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