Paul:
If you are not a purist in your effort to "restore" this tube amp, INSTEAD
of replacing the multi-section electrolytics you can just use "single" axial
lead or radial electrolytics. As long as the multi-section is not shorted
or has excessive leakage you can just leave it in the circuit and connect
the new, single electrolytics to the multi-section electrolytics terminals
underneath the chassis, leaving the top of the chassis looking "original.".
The newer high voltage electrolytic caps will be much smaller than from
decades ago so the job will look quite good. As far as the signal caps are
concerned, I would not bother with them unless you have found degraded
performance or confirmed that the original signal caps are faulty or leaky.
The most important of the signal caps will be the coupling capacitors to the
grids of the power output tubes..... probably 0.1, 0.22, or 0.47 uf @ 400
or 600 V.
Then, of course you will want to test and/or replace the vacuum tubes....
again, the most important will be the expensive output tubes.... and of
course check the preamp tubes for performance and possible microphonics.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


"Paul" wrote in message
news:42555f70$0$3102$afc38c87@...
I have a Scott 299B tube amp which is in need of restoration. It is
complete and unmollested, but probably has not been powered-up for a
decade or two. I would like to replace the signal cap's with
audiophile grade polys to improve reliability and sound. I am also
concerned about the electrolytic cap's so I checked all of them in
circuit with an ESR meter. Out of the 5 multi-segment twist-lock cans,
3 have high ESR. One has 2 sections that are dead, and the other 2
have sections with high ESR (3-9 ohms). I am having trouble finding
replacement cans, and the ones I found are about $30 each. To me, this
thing is not worth $100 worth of 'lytics plus the cost of new poly's,
so I am looking for alternatives. Do I really need to replace the 3-9
ohm ESR parts? 3 of these are 100uF and filter the DC filament voltage
for the preamp tubes. Another is 10uF, measures 5 ohms, and filters
the bias voltage for the output tubes.

Does anyone know of a supplier who has a good selection of multi-cap
cans at lower prices?

The one that is dead is 20/450v, 20/450v, 25/25v, 25/25v, and is 1.4"
dia and 2" high.

The high ESR ones are 100-100-10/75v and are the same size.

Thanks,
Paul

"sofie" bravely wrote to "All" (07 Apr 05 10:32:29)
--- on the heady topic of " Multi-section cap's for Scott 299B tube amp
restoration"

Just a comment I heard the expert on Antiques Roadshow explain that
the integrity of the internal circuits on old equipment has no bearing
whatsoever on value. The real value is in the esthetic cosmetic appeal
and especially the rarity. If it actually operates is only incidental
and nice to know. So I totally agee that it is okay to replace any
defective electros with modern ones.

A*s*i*m*o*v


so From: "sofie"
so Xref: aeinews sci.electronics.repair:45208

so Paul:
so If you are not a purist in your effort to "restore" this tube amp,
so INSTEAD of replacing the multi-section electrolytics you can just use
so "single" axial lead or radial electrolytics.

.... Thomas Edison invented the "Light Emitting Resistor"

"Asimov" writes:

"sofie" bravely wrote to "All" (07 Apr 05 10:32:29)
--- on the heady topic of " Multi-section cap's for Scott 299B tube amp
restoration"

Just a comment I heard the expert on Antiques Roadshow explain that
the integrity of the internal circuits on old equipment has no bearing
whatsoever on value. The real value is in the esthetic cosmetic appeal
and especially the rarity. If it actually operates is only incidental
and nice to know. So I totally agee that it is okay to replace any
defective electros with modern ones.

Though the purists will stuff them into the old cans.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
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| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.

A*s*i*m*o*v

so From: "sofie"
so Xref: aeinews sci.electronics.repair:45208

so Paul:
so If you are not a purist in your effort to "restore" this tube amp,
so INSTEAD of replacing the multi-section electrolytics you can just use
so "single" axial lead or radial electrolytics.

... Thomas Edison invented the "Light Emitting Resistor"

Well of course this is a matter of personal preference, but if it was me I'd replace all of them.

Unlike wine, electrolytic caps defintely do *not* improve with age ;^)

Eric Law

"Paul" wrote in message news:42569874$0$6116$afc38c87@...
Thanks to all who took the time to reply. Unless I find a cheaper
source for replacement multi-cans, I will probably gut the old can(s)
and stuff them with new cap's as Sam suggested. It is a fairly shallow
and crowded chassis, so adding parts underneath would be difficult.

Any comments regarding the need to replace based on the measured ESR
values? If not, I'll probably replace only the dead ones at first, and
see if here is any hum.

On 'lytics that have not seen voltage for many years, I know that I
should bring the voltage up slowly the first time. Should I expect the
ESR to change after the first few charging cycles?

Paul

I restored a 1948 Mantola and used 3 individual electrolytics to
replace the multi-section can. One problem though -- the new
capacitors almost wouldn't fit under the chassis. I had to use kevlar
tape to insulate the cans from the other component leads.

Quote from Asimov:
Just a comment I heard the expert on Antiques Roadshow explain that
the integrity of the internal circuits on old equipment has no
bearing whatsoever on value.

That's good to know! I keep watch on the "book" value of this radio.

"Paul" bravely wrote to "All" (08 Apr 05 14:45:04)
--- on the heady topic of " Multi-section cap's for Scott 299B tube amp =
restoration"

Pa From: (Paul)
Pa Xref: aeinews sci.electronics.repair:45278

Pa Thanks to all who took the time to reply. Unless I find a cheaper
Pa source for replacement multi-cans, I will probably gut the old can(s)
Pa and stuff them with new cap's as Sam suggested. It is a fairly
Pa shallow and crowded chassis, so adding parts underneath would be
Pa difficult.
Pa Any comments regarding the need to replace based on the measured ESR
Pa values? If not, I'll probably replace only the dead ones at first,
Pa and see if here is any hum.

Pa On 'lytics that have not seen voltage for many years, I know that I
Pa should bring the voltage up slowly the first time. Should I expect
Pa the ESR to change after the first few charging cycles?


Paul, the matter of what amount is ESR is acceptable depends on the
expected working voltage and current. Older tube amps used high
voltages with low current and required less capacitance but thicker
dielectrics which typically results in greater ESR than a low voltage
high capacitance electro.

For example in a 350 volt DC supply that has 15 volts of ripple with
50mA, then 7 ohms ESR will add about a negligable 1/3 of a volt.
However, conversely if an electro is used for cathode bypass then that
same 7 ohm ESR might upset circuit conditions significantly.

Further some ESR meters may have a source of error giving a higher
reading with smaller value capacitance due to the test fequency being
too low (adds capacitive reactance to ESR) or too high (adds self
inductance from spiral plates).

On the matter of re-forming an electro, if the seal looks clean then
there is a good chance of success, and yes ESR will decrease a lot
once the electro is re-formed. Just remember a somewhat higher ESR is
to be expected with the higher voltage electros and might be normal.

A*s*i*m*o*v

.... A stereo system is the altar to the god of music.

On Thursday, 07 Apr 2005 22:42:18 -500, "Asimov"
wrote:

Just a comment I heard the expert on Antiques Roadshow explain that
the integrity of the internal circuits on old equipment has no bearing
whatsoever on value. The real value is in the esthetic cosmetic appeal
and especially the rarity. If it actually operates is only incidental
and nice to know. So I totally agee that it is okay to replace any
defective electros with modern ones.


ah.. I'd think that's completely opposite to what the roadshow guy was
trying to get across. The value is the original state.

Working or NOT.

Fixing it (changing it) to make it work will destroy the original
antique value.

You don't re-blue an old gun.