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5881's/KT66's in Heathkit W4-AM
Hello all...
I need a little help. I recently purchased 2 Heathkit W4-AM amps with plans to recap, change resistors, change RCA jacks, etc. The tube complement, according to Heathkit's blurb, are 5881'2, 6SN7's, and 5V4G rectifiers. My questions are these: 1. Are 6L6's and KT88's direct replacements for the 5881's? I understand either is more musical than the standard 5881. Also,the KT66 has higher Va (B+) rating at 500v and the 5881 is lower at 360v. The KT66 has 1.2a heater, while the 5881 a 0.9a heater. Just some guidance or someone's experience. No flaming encouraged... 2. I would like to replace the 5V4's with GZ32's. IS this OK? Upside? Downside? Any help would be appreciated. Try to keep it on a general level. I was in marketing and only appear to speak technobabble well. Best to all, Dave David Stanard Silver Circle Audio Tel: 281 870 8272 Fax: 281 870 8846 Mobile: 832 656 7730 www.silvercircleaudio.com |
#2
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"300B" wrote in message ... Hello all... I need a little help. I recently purchased 2 Heathkit W4-AM amps with plans to recap, change resistors, change RCA jacks, etc. The tube complement, according to Heathkit's blurb, are 5881'2, 6SN7's, and 5V4G rectifiers. My questions are these: 1. Are 6L6's and KT88's direct replacements for the 5881's? I understand either is more musical than the standard 5881. Also,the KT66 has higher Va (B+) rating at 500v and the 5881 is lower at 360v. The KT66 has 1.2a heater, while the 5881 a 0.9a heater. Just some guidance or someone's experience. No flaming encouraged... 2. I would like to replace the 5V4's with GZ32's. IS this OK? Upside? Downside? Any help would be appreciated. Try to keep it on a general level. I was in marketing and only appear to speak technobabble well. Best to all, Dave David Stanard Silver Circle Audio Tel: 281 870 8272 Fax: 281 870 8846 Mobile: 832 656 7730 www.silvercircleaudio.com On paper .. the 5881 and 6L6 are similar ... the 6L6 is very old and reached it's pinnacle with the 6L6GC .. which is roughly equivalent to a 5881 WXT ..... Can you just plug it in ? .. well, depends whether this is a fixed bias or cathode biased amp... need lots more info .. KT88 .. ? .. entirely different animal .. plugs in the same base and gets hot but is nothing like a 5881/6L6/KT66 What comes out ? ..... Who knows .. might sound nice ... who knows ... you are moving away from the original spec This is not Bill Gates.. Plug and Play .. cheers jim |
#3
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"300B" wrote in message ... Hello all... I need a little help. I recently purchased 2 Heathkit W4-AM amps with plans to recap, change resistors, change RCA jacks, etc. The tube complement, according to Heathkit's blurb, are 5881'2, 6SN7's, and 5V4G rectifiers. My questions are these: 1. Are 6L6's and KT88's direct replacements for the 5881's? I understand either is more musical than the standard 5881. "More musical?" I keep hearin' that, been a player for 17 years, a music freak for as long as I remember, but still don't know what that means. Could you explain? Or is it one of them "je ne sais pas" thing? 5881's are nice, small glass bulb tubes, think kind'o mil-spec 6L6, and, i bet the plate rating'spretty conservative. (in general US #### tubes are mil-spec, or tighter spec, or somehow "improved" (lower noise, lower hum, better voltage design maximums, etc., etc.), than their #letter# equivalents. I use all the ones that I can find that match in fender twins (guitar amps), where they're driven past their ratings, and I'm yet to see a failure. I don't think they make real 5881's anymore - they just name them 6L6xyz, they're plug -in replacement for 6L6(wahtevers). Bias out about the same, and, since you ain't going to have much of a selection in 5881's, go with 6L6's. Also,the KT66 has higher Va (B+) rating at 500v and the 5881 is lower at 360v. The KT66 has 1.2a heater, while the 5881 a 0.9a heater. Just some guidance or someone's experience. No flaming encouraged... First, see if KT66's *physically* fit - them's big suckers. Shoo' 'purty, though, and someone has re-issued them. I have no idea what the real transformer heater winding ratings are, but I *REALLY* doubt you'll run into trouble there. (just for giggles, i looked at the schematic - the heater taps are rated at 4A, so you're free & clear 'nless you're actually going to use the preamp sockets... The minus? Price, size, the UL setup may want a resistor on the SG's and become unstable (or not), absurdity (you ain't gonna get more power - they'll fit in the socket, do the job, bias out a bit differently, but it's one of those "should I swap my EL34's for 6550's" questions. Replace the tubes with what the amp calls for - if results are less than satisfactory, look at the schematics, look at similar schematics, and try to figure out what could be done. At first glance, the amp's a very standard, tried & true design - I'd probably try upping the value of the cap after the choke (I'm sure that value was dictated by cost & possibly it being a section of a can - caps are cheap & small now), and try to figure out the intent of the input circuit (right after the input jack there's a 15K R followed by a ... .05/400 C, before the signal sees the standard 15k snubber R preceeded by a 470K grid leak R - a head-scratcher... Perhaps intended to be driven by a heath preamp with odd output characteristics - or I could be missing something ... or it could be a misprint (http://www.freeinfosociety.com/elect...eathkitw4m.htm l). Finally, asking for advice - all of which may be of dubious quality (including mine), and discouraging flames is ... worse than pointless. You're not going to make any real money hot-rodding amps, especially if your (admittedly) limited tech knowledge forces you to ask for advice on NG's like RAT, so why not have fun, and figure these things out yourself? Those heathkit amps are almost ideal learning platforms - 2 monoblocks, with standard tubes, simple to understand circuitry, and you have 2 identical amps - make a change in one, annd compare! presto. Screw one up, and all you have to do ape the other one, to bring it back. Have fun, and good luck. -dim (Say, what do you guys like better, Rubycon or nippon chemi com? Are Elnas really better? What about Mepco /Centralabs? I found that the staging improved dramatically if I kept them in the *bottom* milk crate, but old Illinois lytics are still my choice for Jazz vocals, especially if used in older bench PS's placed in the basement.) in marketing and only appear to speak technobabble well. Best to all, Dave David Stanard Silver Circle Audio Tel: 281 870 8272 Fax: 281 870 8846 Mobile: 832 656 7730 www.silvercircleaudio.com |
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