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

"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

"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