1. Home
  2. Electronics Repair
  3. Re: Multi-section cap's for Scott 299B tube amp restoration

Re: Multi-section cap's for Scott 299B tube amp restoration

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

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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
Reply to
sofie
Loading thread data ...

Though the purists will stuff them into the old cans. :)

--- sam | Sci.Electronics.Repair FAQ Mirror:

formatting link
Repair | Main Table of Contents:
formatting link

+Lasers | Sam's Laser FAQ:
formatting link
| Mirror Sites:
formatting link

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.

Reply to
Sam Goldwasser

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

Reply to
EL

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.

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

Reply to
tlbs

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.

Reply to
tobacco_talk

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.