Jim, I respect your opinions re the H-K amps. However in support of my contention re the superiority of 6SN7's one can simply research prices...the market does not lie. (Even Fullmusic has come out with a fancy 6SN7; the new 6CG7 is a cheezy E-H) The 12BY7 was not intended to be an audio tube for low level amp; the EF86 was so intended; AND the OG 5-10/20 used them. Vintage 1940's early '50s chrome dome tri plates are going to look very good on the amp; and they have NEVER let me down in terms of sound quality. The voltage levels on the amp are crying for me to use 6550s; new production 6L6/7581/7027s are real iffy at the voltages that I am seeing with the rebuilt power supply. There is a Cit V on the auction site right now running a set of cheap Chinese '6l6GC's the guy even lit the thing up. Fortunately the 3.3-Ohm cathode resistors should save the OPTs on that amp...
Sorry, I don't agree. First off prices are as much supply/demand as anything else. Othewise why would NOS 6386s go for $400 bucks or more!
The 6SN7 was an oscillator in TV sets. The whole idea of "audio tubes" is amusing to me - as if the tubes knew or only performed right - in their "designated" circuits. Some tube types do have attributes that make them more useful for certain applications, but that's about it other than a few tubes that were indeed optimized for audio use - the 7199, the 7591 & 7868, and there's a few others.
BTW, have you ever heard a 6CG7 EH? Is it the best ever? No. Is it a darn good tube? Yes, no doubt about it.
New production 6L6GCs and such are just fine at the voltages in a Cit V. I recommend the SED 6L6GC, the Tung-Sol reissue 6L6GC-STR or 6L6G. Or the Russian NOS 6P3S-E. All do just fine in the Cit V - I know from first hand experience.
6550s draw way more heater current than the power trafo can provide reliably - you need almost 3 amps more to run them.
I'm not going to reply anymore - but it seems you have adopted as fact a number of the fables that swirl around the Citation gear (and current production tubes). As I said before - it's your amp, do what you want. But you are basing a lot of your planning on what I believe is misinformation, and I thought you should know that before any holes get punched and you can't go back.
my thoughts too....
i get mine for free......discarded ATX psu's have those......the crt computer monitor likewise is a good source for parts.....
Bob Carver used this tube in his high-end CARVEr Silver sevens ..http://hometheaterreview.com/carver-silver-seven-mono-vacuum-tube-power-amplifier-reviewed/ ....why do you think he did that?
i think you have been reading the wrong stuff from the internet....read here more often, you will learn a lot....
Oh and BTW I was one of the original staff members of VTV magazine; along with Eric Barbour and the late Charles Kittleson. We did numerous listening tests of various preamp and output tubes. The older octal tubes generally would outperform newer novar types; mostly because the newer types were designed with low cost in mind...
Bob Carver used this tube in his high-end CARVEr Silver sevens ..http://hometheaterreview.com/carver-...fier-reviewed/ ....why do you think he did that?
i think you have been reading the wrong stuff from the internet....read here more often, you will learn a lot....
Looking at the DATA SHEET for the EF86; Microphonics are prominent in the specifications; also ther is an internal shield. 12BY7...NOPE. I don't know what may be in another designer's mind when choosing tubes but I like to go by the data sheets; not 'reading the wrong stuff from the Internet'
Anyway I am starting to go over the front end now that the power supply and rear panel are completed. My design criteria for the driver is that it should provide at least double the swing required by the drive tubes. The Cit V front end falls far short of that spec, and the components are really old and out of spec. Anyway once I get through with the mods I will post again.
i think you have been reading the wrong stuff from the internet....read here more often, you will learn a lot....
Looking at the DATA SHEET for the EF86; Microphonics are prominent in the specifications; also ther is an internal shield. 12BY7...NOPE. I don't know what may be in another designer's mind when choosing tubes but I like to go by the data sheets; not 'reading the wrong stuff from the Internet'
Anyway I am starting to go over the front end now that the power supply and rear panel are completed. My design criteria for the driver is that it should provide at least double the swing required by the drive tubes. The Cit V front end falls far short of that spec, and the components are really old and out of spec. Anyway once I get through with the mods I will post again.
Finished the rebuild. I dremel'd a single sided copper clad to build the power supply. Went Hexfred's and NTC inrush limiter feeding the 1200 uF 250V caps. I noted the lack of 6CG7 driver headroom, so I beefed up the bias supply to a full bridge and used it to pull the driver tail so as to increase current. Finally after some thought I yanked all that out and went with my long tail 6BN11 twin pentode driver. This allowed me to run output tube plate-grid feedback loops and eliminated the stability problems on the low frequency side as well (both drive grids are ground referenced). With the simpler but beefier drive stage the output xfmr is dictating the frequency response which now extends to over 200 kHz with no peaking. With all the extra room I put a screen grid dropping circuit consisting of a few 15V SMA Zeners to get the screens into tube manual operating range.
did you ditch the 12by7 input stage? or just replaced the 6CG7's? and did you operate the 6BN11 pentode or tiode? sorry for the questions....
i haven't tried the 6BN11, i have a lot of those purchased at the Rogalskie's for a dollar a pop, i suspect they sound good....can you post schemes? thanks
I am attempting an upload. Usually one needs to put a 30 pf or so cap from the 2nd (the one with the grounded grid) drive tube plate to ground to suppress 1-2 MHz seen on output when the load is disconnected. Thanks for the tip; I had forgotten where I got the 6BN11's from; ordered another 50.
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Nuvistordave,
What's the input sensitivity and max ouput swing of your 6BN11 dif amp stage? I'm looking for a driver to swing about 130V rms at each anode of a 6336A (triode in push-pull for a total of 260V rms) for about 20 Watts out - and I have a couple of pairs of 6BN11 with matched sections .... what do you think?
What's the input sensitivity and max ouput swing of your 6BN11 dif amp stage? I'm looking for a driver to swing about 130V rms at each anode of a 6336A (triode in push-pull for a total of 260V rms) for about 20 Watts out - and I have a couple of pairs of 6BN11 with matched sections .... what do you think?
I thought 130VRMS sounded like an awful lot. Running around 250V on the plates you would need a 400V drive B+ and about -130V for the long tail bias; 10K LT resistor. Assuming 30K plate resistors and 50K grid return resistors the plate current is 5 mA and total plate load is about 19K. So the tubes should be able to run 75-80V peak under those conditions. The gain is still very good (those are the conditions I use to drive 6550's) Note that I am running separate SG bias circuits on the 6BN11's. That is a great help in balancing the tube halves. The AC Bal resistor is absolutely necessary as well.
The sound...well all I can say is that the stability of the circuit is quite clearly heard. Note also that I am not having to throttle the front end frequency response as on the original 5-20; the OPTs are thus able to breathe freely. And a a buck a pop the 6BN11's are a great buy indeed.
The sound...well all I can say is that the stability of the circuit is quite clearly heard. Note also that I am not having to throttle the front end frequency response as on the original 5-20; the OPTs are thus able to breathe freely. And a a buck a pop the 6BN11's are a great buy indeed.
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