http://www.audiobanter.com (rec.audio.tubes) Discussion of vacuum tube audio equipment, including hi-fi, guitar (and other instrument) amplifiers, radio circuits, theory and design, vintage and modern equipment, repair/ modifications/ restoration and recommendations. en Tue, 07 Sep 2010 08:09:00 GMT vBulletin 60 http://www.audiobanter.com/images/002/misc/rss.jpg http://www.audiobanter.com http://www.audiobanter.com/showthread.php?t=124809&goto=newpost Sun, 05 Sep 2010 20:43:48 GMT Time to return to tech-talk. In a modest-sized room (by horn standards anyway) I want to rig up a singleton of my modded semi-Fidelio bicor horns for Lowther... Time to return to tech-talk.

In a modest-sized room (by horn standards anyway) I want to rig up a
singleton of my modded semi-Fidelio bicor horns for Lowther PM6A. I
thought I'd do the monoing in a specially made 1 metre cable between
the CD player and the power amp.

The QUAD CD expects to see at least 10K impedance on its outputs.
Output of the CD player is 2Vrms and about 0.5Vrms of that is required
to drive the amp to enough power to handle the horns, so high value
resistors can be used in the monomaker if there is any advantage to be
gained.

However, the sound is NOT intended to be reprocessed as stereo
downstream (home installation, not studio); if I want stereo again,
i'll just plug in a stereo cable.

The pot on the integrated amp is probably (the board won't be here
until Tuesday and i can't read the spec on the piccie) 50K Alps but I
can replace it with a DACT of which I have a good selection of values.

So what value resistors would you use for monoing?

How many? Only two, or three?

With your choice of values, what can I expect to lose from the monoing
in bandwidth as distinct from gain?

Andre Jute
Visit Jute on Amps at
http://www.audio-talk.co.uk/fiultra/
"wonderfully well written and reasoned information for the tube audio
constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site containing vital gems of
wisdom"
Stuart Perry Hi-Fi News & Record Review
]]> Vacuum Tubes http://www.audiobanter.com/showthread.php?t=124809 http://www.audiobanter.com/showthread.php?t=124790&goto=newpost Fri, 03 Sep 2010 21:42:52 GMT Does anybody know there's a (definitive and consistent) temperature
dependence for pentode grid voltage like there is for MOSFET threshold
voltage?

Reason being I'm contemplating grid drive with a MOSFET follower and
wondering if I should bother worrying about temp compensating the
MOSFET threshold drift.
]]> Vacuum Tubes flipper http://www.audiobanter.com/showthread.php?t=124790 http://www.audiobanter.com/showthread.php?t=124769&goto=newpost Thu, 02 Sep 2010 11:33:21 GMT wrote: > In article > <68f4631a-fb50-45e1-8d23-d6ed908a7...@t5g2000prd.googlegroups.com>, > *Patrick...]]> On Aug 30, 1:05*am, John Byrns > wrote:
> In article
> >,
> *Patrick Turner > wrote:
>
> > That is an impressive tubed stereo receiver. If it is a 1960 model
> > then does it not predate the addoption of the Zenith-GE multiplexing
> > for stereo info using a 38kHz sub-carrier?
> > I searched for a free online available schematic for the S-8000 which
> > this receiever seems to be. Probably it is after 1961 and with the
> > addopted standard MPX stereo decoding circuits of the time. Anyone
> > bidding for this would be able to check this out because you have a
> > picture of the front cover of the owner manual.
> > I could not find a free schematic although someone was able to sell a
> > service manual for just about all Sherwoods from those ancient times.
>
> The top of chassis view clearly shows the presence of a post June 1961
> Pilot Tone Stereo decoder.
>
> > These old sets usually develop a number of faults over the years. It
> > happens also with Scotts and Fishers et all. But they do respond to
> > having all dud tubes and R&C parts replaced along with some upgrade to
> > electrolytic cap values, and some possible revisions to output tube
> > biasing methods.
>
> What revisions do you recommend to the output tube biasing methods? *
> Most of these old receivers originally used a "fixed bias" scheme.

I cannot see the full schematic of the receiver in question.

But many such things were seriously compromised by very poor bean
counter inspired biasing of OP tubes.

It was common practice to use the heater filaments of the phono
stages for the common cathode resistance for all 4 output tubes so
that you could have Ek at every OP tube at +25V at a total Ia = 300mA,
if there were 4 x 12AX7. Trouble occurs when OP tubes drift and don't
all bias the same with Ia variations of +/- 70% as I have seen in bad
cases.

Almost none of the well known brands used separate individual RC
cathode biasing for each OP tube which was the most user friendly
method. None I know of ever had separate trim-pots to set the fixed
bias which most owners got wrong causing smoke and burned out parts.

As I have so often said, much of the design methods used in 1960
receivers was bloody crook ****e, and they always used a minimum cost
design method which meant poor lowest common denominator performance.

Patrick Turner.

>
> --
> Regards,
>
> John Byrns
>
> Surf my web pages at, *http://fmamradios.com/

]]> Vacuum Tubes Patrick Turner http://www.audiobanter.com/showthread.php?t=124769 http://www.audiobanter.com/showthread.php?t=124765&goto=newpost Wed, 01 Sep 2010 18:44:29 GMT I'll probably sell my two KT88's.

http://en.wikipedia.org/wiki/KT88

I am taking the tubes to a friend who has an AVO VCM MK1 valve tester to
test their condition.

What will an audiophile like to know so he can have a good idea what he
or she would be buying? I want to describe the items so a buyer knows
the state of the tubes.

Thanks.
]]> Vacuum Tubes http://www.audiobanter.com/showthread.php?t=124765 http://www.audiobanter.com/showthread.php?t=124768&goto=newpost Wed, 01 Sep 2010 18:35:48 GMT I'll probably sell my two KT88's.

http://en.wikipedia.org/wiki/KT88

I am taking the tubes to a friend who has
]]> Vacuum Tubes http://www.audiobanter.com/showthread.php?t=124768 http://www.audiobanter.com/showthread.php?t=124763&goto=newpost Wed, 01 Sep 2010 13:02:42 GMT Even worse, we shouldn't have a system where people with defective genes > (the homos) are reproducing using these defective genes by artificial means, > or...]]> > Even worse, we shouldn't have a system where people with defective genes
> (the homos) are reproducing using these defective genes by artificial means,
> or otherwise.
>
> This just continues the genetic defect.
>


Defective genes? Look in the mirror.
]]> Vacuum Tubes Keith http://www.audiobanter.com/showthread.php?t=124763 http://www.audiobanter.com/showthread.php?t=124755&goto=newpost Wed, 01 Sep 2010 06:55:20 GMT e mail geld verdienen , ich im internet geld machen , guild wars schnell geld verdienen , geld umfrage , ganz leicht geld , einfach geld verdienen im internet... e mail geld verdienen , ich im internet geld machen , guild wars
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]]> Vacuum Tubes lucky-villa http://www.audiobanter.com/showthread.php?t=124755 http://www.audiobanter.com/showthread.php?t=124746&goto=newpost Tue, 31 Aug 2010 19:52:17 GMT Found two GEC KT88 tubes in the attic, (not boxed).

In the rectangle, below the designation "KT88" is, I think, a date and
manufacture code of: "RB Z"

Anyone know when these were manufactured?

They are similar looking to:

http://www.natubes.com/data/images/p.../large_517.gif
]]> Vacuum Tubes http://www.audiobanter.com/showthread.php?t=124746 http://www.audiobanter.com/showthread.php?t=124738&goto=newpost Tue, 31 Aug 2010 05:27:51 GMT Is there anyone who likes to talk about tube audio anymore or is this another social issues sight. Is there anyone who likes to talk about tube audio anymore or is this
another social issues sight.
]]> Vacuum Tubes sortech http://www.audiobanter.com/showthread.php?t=124738 http://www.audiobanter.com/showthread.php?t=124731&goto=newpost Mon, 30 Aug 2010 17:46:11 GMT I see your test. Eh? What test? Ian]]> Patrick Turner wrote:

>I see your test.


Eh? What test?

Ian


]]> Vacuum Tubes Ian Iveson http://www.audiobanter.com/showthread.php?t=124731 http://www.audiobanter.com/showthread.php?t=124737&goto=newpost Sun, 29 Aug 2010 00:47:17 GMT Restored Antique Radios FS



http://www.a383ina68.addr.com/radiorest/main.htm



Just be sure to click on the "Radios for sale icon" to view the sets!





These investment quality Fully Restored radios will give you the advantage
of a set that has indeed been RESTORED, and not simply fixed, repaired,
spiffed up, or outsourced to another servicer or refinisher for work.

I have 29 years of experience in Antique Radio restoration and combine that
with my full time day job of MRI coil and system development and expertise
in Failure analysis to produce a restoration that has had detailed
attention given to each part of the radio, and not just a simple gutting of
the electronics or recapping of the chassis.

Each questionable part is replaced, wiring is examined, all tubes
are tested and replaced if necessary, mechanical assemblies are
disassembled, cleaned, relubed and aligned. Each set also gets a new
powercord that is grounded or polarized and an AC line fuse is added if not
already equipped.

Cabinets get detailed veneer repair and replacement if necessary
from an extensive inventory of vintage veneer, dial bezels are restored,
each knob is refinished or detail cleaned, Photofinish is recreated if
necessary and 7 coats of hand rubbed finish are applied. The result is
stunning and gives the purchaser a set that will be around and working for
many, many, years to come. Please visit the above website for even more info
about me and my restorations.



My Restorations are just what you're looking for if you want a set that
looks and works as new. These are completely redone, not only part of the
cabinet is refinished and another part left cobbled up, the entire unit is
restored. These restorations are not simple "Recappings with a new power
cord" I tend to every part of the chassis that needs attention, cleaning and
relubing mechanical parts, rebuilding of dial assemblies, detailed
refinishing or cleaning of knobs and bezels and any specific needs of a
particular chassis. My sets are not "over restored", I don't rip every
component and wire from the chassis and replace it just because its old,
these sets are preserved in as much of their original state as possible to
keep them reliable and safe. 30 years of doing antique radio restoration
goes into knowing just what needs to be done and just how it should be done
when I restore one.



Thanks!!



Keith Park




]]> Vacuum Tubes Keith Park http://www.audiobanter.com/showthread.php?t=124737 http://www.audiobanter.com/showthread.php?t=124685&goto=newpost Thu, 26 Aug 2010 20:47:42 GMT > Even worse, we shouldn't have a system where people with defective genes > (the homos) are reproducing using...]]> Soundhaspriority ( the real one ? )wrote:
>
> Even worse, we shouldn't have a system where people with defective genes
> (the homos) are reproducing using these defective genes by artificial means,
> or otherwise.

I know there's a 'redhead gene' but one for homosexuality ? How about
bisexuals too ? False argument methinks.

Graham
]]> Vacuum Tubes http://www.audiobanter.com/showthread.php?t=124685 http://www.audiobanter.com/showthread.php?t=124570&goto=newpost Mon, 16 Aug 2010 14:37:21 GMT Recently my amps trannies were melted when the 211 failed. With less than 150 hours on the tube but past the 30 day warrantee. I bought the tubes in Oct.... Recently my amps trannies were melted when the 211 failed. With less than 150 hours on the tube but past the 30 day warrantee.
I bought the tubes in Oct. 2009 from Grant Fidelity. however never used them until well after the 30 day time frame. Which Grant was aware of.
One tube shorted and took out the output and high voltage trannies. Costing me $1500 to repair.
Neither Grant Fidelity nor Full Music will care after the 30 days expires. For $500 one would think that the Manf. or north American distributor would make ammends because of the damage done. Something fishy going on as the distributor.
No no and no is the answer from them. Buyer beware. Stay away.


charles ]]> Vacuum Tubes charles rollo http://www.audiobanter.com/showthread.php?t=124570 http://www.audiobanter.com/showthread.php?t=124535&goto=newpost Fri, 13 Aug 2010 09:30:10 GMT I have just received a prototype PCB that I need to cut accurately to size (double Eurocard). This is well beyond my poor hack sawing skills so I am hoping... I have just received a prototype PCB that I need to cut accurately to
size (double Eurocard). This is well beyond my poor hack sawing skills
so I am hoping there is someone not to far from me (Holt, UK) who has a
band saw or something similar that I can use.

Help?

Cheers

Ian
]]> Vacuum Tubes http://www.audiobanter.com/showthread.php?t=124535