Newer sprague atom 20uF 600V caps are really long!

[TubeGeek]

I am working on a couple blonde fenders and have a bit of an issue.  The Sprague caps I ordered are too long for the doghouse.


It has been a few years since I have had a blonde in for service but I recall the caps fitting inside the doghouse back then.


The new caps are not cheap either. I am in Canada so by the time I have them in my hands, they are almost $60 each.


The price of parts is insane for canucks.


Anyhow…anyone run into this before?


My thoughts are to install the caps and insulate the + leads and just leave the doghouse off. I don't like this but it might be ok.


The other option is to install F&T caps which are rated for 500V.  The plate voltage is measuring 492VDC, so pretty close to max.


https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_6g6a_schem.pdf

[glass54]

Join the Club!! $$$ and dimension problems.
I can't see exactly, you might have to take an overhead shot of PS board, but you might need to resort to 2 Caps/resistors in series for PS input cap, using something like 80u/100u rated at 350V plus. 220k Metal Oxide 1W across each one for correct Volts sharing and bleeding.
See example attached
Regards
Mirek

[tubeswell]

I'm thinking they probably have 2 caps in series inside that 600V cap skin

[TubeGeek]

I'm thinking they probably have 2 caps in series inside that 600V cap skin

I swear this new batch of sprague is longer than it used to be so I wouldn't doubt you're right.


I remember waaaay back when I was first learning about sprague caps, I opened one up to see what was inside and it was a small cap inside a big tube. I still have it around for reference.

[HotBluePlates]

... The Sprague caps I ordered are too long for the doghouse. ...

I'm thinking they probably have 2 caps in series inside that 600V cap skin

On another forum, someone else encountered the same problem with a brownface Showman.  They wound up ordering 350v axial caps (F&T/Mersen, I think?), but had a brief flirtation with using 47µF 350v radial caps in series for each filter cap position.  Turns out the radial caps were short enough that the completed filter cap board fit inside the doghouse.

As guessed, the Sprague caps are 2 caps in series inside the wrap.  The photo below is a 1989 dated-coded cap (which also was too long to fit under the doghouse cover).

[punkykatt]

What is the total length of the Sprague cap?

[HotBluePlates]

What is the total length of the Sprague cap?

Almost 4 inches.

Meanwhile cap pans are on the order of 3.5 inches.

[punkykatt]

Cut the dog house in the center length wise. Move the one half of the can the distance you need, drill new holes and remount. Or build a new dog house using 2"x 1/16" thick aluminum angle, assemble with pop rivets  drill new holes and mount with angle brackets. I`ve done that before.

[SteveInMN]

I'd be inclined to rotate them 90 degrees and see how that works. I bet they'd fit that way. You might need to zig-zag them.  You'll need a fresh board, but it would avoid serious bodging and/or unsafe conditions (I'd be really, really concerned about leaving them uncovered. Like REALLY concerned).

[Willabe]

It has been a few years since I have had a blonde in for service but I recall the caps fitting inside the doghouse back then.

The 600v Sprague caps have always been long.

The new caps are not cheap either. I am in Canada so by the time I have them in my hands, they are almost $60 each.

I stopped using the blue Sprague caps a long time ago because of the price. Went to F&T's.

My thoughts are to install the caps and insulate the + leads and just leave the doghouse off. I don't like this but it might be ok.

I wouldn't take that chance, your asking for trouble. Those are the highest voltages in the amp.

The other option is to install F&T caps which are rated for 500V.  The plate voltage is measuring 492VDC, so pretty close to max.

I like the F&T's, their great caps, price is pretty good. I also like using modern radial caps on new builds, small, great price.

Schematic shows 470dcv on the plates of the 5881/6L6GB. You measure 492dcv. So wall acv is probably high, and/or the tubes are biased on the cold side, drawing less current, dcv will rise.

So, 2 @ 350v caps in series, with the voltage sharing R's, is probably what you need.

Unless you can get the dcv down to ~470dcv. Then you could use 2 @ 22uF @ 500v. 

F&T makes 100uF @350v and 22uF @ 500v.

If the plate dcv comes down after you set the bias. And if the owner has a variac tell him to use it.

Weren't the blond amps run at 117ac wall voltage?

[TubeGeek]

Appreciate the responses so far.


I do keep stock of both generic and F&T caps for repair work. I jumped the gun on this job and ordered the sprague's, not realizing the sizes.



My plan right now is to work with a buddy to 3D print a new doghouse that will accommodate the sprague's since I've already ordered the new caps.

[bartman]

Back when Doug had the full line of Sprague caps there was a note that the 600v caps were too long to fit under a Fender doghouse.

[TubeGeek]

Back when Doug had the full line of Sprague caps there was a note that the 600v caps were too long to fit under a Fender doghouse.

It’s clear that my memory was not correct.

[mresistor]

Tube Geek  - Dave at Just Radios which is in Canada has 600V electrolytic capacitors for a reasonable price and I know everything he carries is good quality. 
https://justradios.com/


Wish I would have known you were ordering two of those 600v Sprague monsters as a few years back a larger Fender amp came to me for repair and it had two of those under the dog house mounted lengthwise with heat shrinked long leads winding all over the place. 

[Willabe]

Dave at Just Radios which is in Canada has 600V electrolytic capacitors for a reasonable price and I know everything he carries is good quality.

It doesn't say how large/long the 600v caps are.

Any ecap rated at 600v is probably has 2 caps inside the can in series to get the 600v rating, so it will be long.   

[mresistor]

Here is a modern axial electrolytic capacitor   no reason why they can't be smaller   example is the mod lytics

[TubeGeek]

Here is a modern axial electrolytic capacitor   no reason why they can't be smaller   example is the mod lytics

And I just received the new 3d printed doghouse 


That would've been much easier.


Thank you for the link. I'll keep that for future use.

[TubeGeek]

Ok….


The new doghouse just arrived at my doorstep.  I loosely fit the caps under and secured the doghouse down.  It looks like it is going to work out.


I did not solder the caps yet, just in case it did not work and there's a chance I could return the caps and go with another route.


Here is a pic. I think I am safe to install the caps now.


What do you guys think?


We extended the doghouse a half inch to the left and also a half inch to the top.

[shooter]

aluminum or plastic??
plastic might get a 'lil soft near the tubes, even with cans on

[TubeGeek]

aluminum or plastic??
plastic might get a 'lil soft near the tubes, even with cans on

Plastic.  I am hoping heat won't be an issue with the preamp tubes.


The caps are soldered and the doghouse fits.  Not the most ideal solution in my opinion but I made the best out of what I got myself into.

[Willabe]

Here is a modern axial electrolytic capacitor   no reason why they can't be smaller example is the mod lytics.

Back in the 90's, the story was that Sprague got a big contract from the US military for ecaps.

The military wanted Sprague to keep the large size on all the ecaps because the length including the leads fit the military gear without any mods.

The vintage guys loved it becuse they fit the old Fenders.

But then the price for Sprague's went through the roof!

[TubeGeek]

After realizing there actually are 600V axial caps available for this amp and I can use the original doghouse…that’s the route I’m taking.  If this were my amp, that’s what I would want if I was paying someone to do the work. Maybe I can put these spragues to use someday.


The 3d printed doghouse did work well but original is better. This is not a blues junior.



I ended up placing a decent order from just radios.  All the common values in 500v, 160v and 50v values.
I like the fact I am supporting a fellow Canadian business right now too. With everything going on right now and all.

I’ll now stock generic 450v, f&t 500v, and these meic 500v caps for repairs that come my way. 


This amp works and does sound good.  I had some fun playing it tonight. 


I’ll update when I get the new caps installed.

[TubeGeek]

Just a little difference in size

[Willabe]