67 plexi 100W (RIFA recap)

[Gaston Gagnon]

Would you believe, I hear ghost notes more than before !!!!!! Is it because they are new ?
When I bought the amp, the filter caps were not original; they were Sprague ATOM lytic TVA-1711 30uF 450V.
Now has brand new RIFA 33uF 450V.

Is it normal to hear more ghost notes ?

The tone is just a little bit more bright but still "amazing" (for me!).

Anyone had this experience after recapping a plexi 100W ?

 

[Matthews Guitars]

I think 33s are marginal or below the real demand for a 100 watter. There's got to be a reason why Marshall went with dual 50 caps for the 100 watt Superleads, which cost more than 33s. Marshall never spent money they didn't have to spend.

Strap some 15 uF caps across the Rifas as an experiment. If that solves the ghosting problem, I'd say to just go with it. No need to replace the 33s with 50s if the Rifas plus some 15s will do the job.

 

[Pete Farrington]

Checking the actual capacitance of all the caps in question may be illuminating; tolerance to nominal value for ecaps can be pretty wide.

 

[playloud]

Are you sure the RIFAs are brand new? From what I can gather, they stopped production some years ago, so the ones you find for sale now are really "new old stock". They may have drifted out of spec over time - I know Valvestorm reform the ones they sell.

 

[neikeel]

The 67 (is yours the one with 8 caps on the board) are all under filtered from a technical point of view.
I put x4 Rifa 68uF caps just on the mains section and that helped, keeping the others at 33uF kept the feel.
What did you do for the preamp can?

 

[Gaston Gagnon]

The 67 (is yours the one with 8 caps on the board) are all under filtered from a technical point of view.
I put x4 Rifa 68uF caps just on the mains section and that helped, keeping the others at 33uF kept the feel.
What did you do for the preamp can?

Yeah, the one with 8 caps all under.
There was not enough room on the filter caps board for these 8 Spague caps so there was 2 more installed away from these six.
I think I made a big mistake by changing the filter capacitors in my amp.
I might try to reinstall those "messy look" Sprague caps here.

Thank you all for your help.

 

[Seanxk]

Did you re-form the Rifa' before install?, you'd be surprised how much this helps a cap, I re-form even a brand new F&T, once done they perform very well and why wouldn't you except you need up to 500VDC to do it.

 

[Gaston Gagnon]

Did you re-form the Rifa' before install?, you'd be surprised how much this helps a cap, I re-form even a brand new F&T, once done they perform very well and why wouldn't you except you need up to 500VDC to do it.

No, I didn't. I thought they were ready to go !
Now to re-form those caps, I need a dc power supply from 0 to 500 Vdc ?

Old pix (from 1995) are on the Amp Archives site: serial 10245
Since those pix, a Marstran OT replaced the earlier non original OT.

 

[neikeel]

Safest is tubes out and variac gradually increasing input voltage by 10v an hour
On a JTM45 it’s simple just clip 100k resistor across the HT switch and wait until voltage drop across resistor is <5vdc.
On this amp with dual rectifier and centre tapped PT it is too fiddly.

 

[Seanxk]

As the cap's are already in, perhaps as @neikeel says is easier, but if your caps are out and you can borrow a re-former that's good, if not, yes you need a variable 0 to 450/500 Vdc. There's plenty of info online and usually the best is the simplest, mine was made by a friend and is a supply and a 10K ( I think ) wire wound resistor with contacts for a couple of DMM's ( Volts & mA ) and + - for the cap.

Go to page 19 here, where ironically Sencore give an option as explained....

https://www.csulb.edu/sites/default/files/groups/college-of-engineering/About/sencorlc53_z-meter_operation_maintenance.pdf

 

[neikeel]

Only need to go to 120vac in US or 250vac in in U.K.

 

[Gaston Gagnon]

Thanks everyone, I finally order 8 RIFA caps (reformed and ready to go) from Valvestorm. Less pain and trouble... Now hoping that my amp will be healthier this time !
Thanks Seanxk for helping me understand more about electrolytic capacitors.
Thanks also to "playloud" on where to get "reformed and ready to go" caps.

later
Gaston

 

[playloud]

Thanks everyone, I finally order 8 RIFA caps (reformed and ready to go) from Valvestorm. Less pain and trouble... Now hoping that my amp will be healthier this time !
Thanks Seanxk for helping me understand more about electrolytic capacitors.
Thanks also to "playloud" on where to get "reformed and ready to go" caps.

later
Gaston

That works too. I tested the RIFAs I received from Valvestorm for capacitance and ESR, and all were within spec.

 

[Smokie 54]

Would you believe, I hear ghost notes more than before !!!!!! Is it because they are new ?
When I bought the amp, the filter caps were not original; they were Sprague ATOM lytic TVA-1711 30uF 450V.
Now has brand new RIFA 33uF 450V.

Is it normal to hear more ghost notes ?

The tone is just a little bit more bright but still "amazing" (for me!).

Anyone had this experience after recapping a plexi 100W ?

No, it is not normal to hear more ghost notes after replacing the filter caps. There's something else going on.

Stick to the stock values. 33uF 450V is fine.

 

[Gaston Gagnon]

No, it is not normal to hear more ghost notes after replacing the filter caps. There's something else going on.

Stick to the stock values. 33uF 450V is fine.

The amp was working pretty well before; I post a recent video not a long time ago (before I changed the Sprague filter caps for RIFA's (go to 1m57s to hear the lead part): https://www.marshallforum.com/threa...o-a-1967-marshall-super-lead-100-watt.127003/

 

[Gaston Gagnon]

Grrrrrrrrrrrreat tone with my second set of RIFAs (reformed) ! Now my amp sounds as great as before the restoration. Just a bit of "pleasant" ghost notes while playing at max volume, not interfering with the main notes played. I'm so glad...
Thanks to everyone who helped me getting my amp back on the track and strong !

Gaston

 

[playloud]

Excellent! That should keep you going for a while

P.S. I would still be tempted to reform that original set. If you don't want the hassle, perhaps sell to someone with a variac?

 

[Gaston Gagnon]

Excellent! That should keep you going for a while

P.S. I would still be tempted to reform that original set. If you don't want the hassle, perhaps sell to someone with a variac?

When I bought the amp (almost 30 years ago), the filter caps were not the original ones in the amp; they were the Sprague 30uF 450V in it. I always wanted to changed them, but was afraid to loose the tone.
Now I'm very happy with the reformed RIFAs.

p.s. Variac is a must with this amp; met a Marshall specialist in Montreal a long time ago, he said to me: "if you want to keep playin' this amp, run it at 110-115V, not over"

 

[playloud]

When I bought the amp (almost 30 years ago), the filter caps were not the original ones in the amp; they were the Sprague 30uF 450V in it. I always wanted to changed them, but was afraid to loose the tone.
Now I'm very happy with the reformed RIFAs.

p.s. Variac is a must with this amp; met a Marshall specialist in Montreal a long time ago, he said to me: "if you want to keep playin' this amp, run it at 110-115V, not over"

Oh, I didn't realize you already had a variac. In that case, I would definitely recommend reforming the original set of RIFAs when you have some downtime in future.

Glad it worked out either way!