350B(2000s) Recap & cap upgrade

[BassHog]

So I did a recap on my 350B(Solid State rectified 2000S) head last weekend and I wanted to beef up the cap values to 50uf per stage similar to what the SDS labs Capacitor boards do but at a much more reasonable cost.
The SDS boards take up a lot of space and are pretty spendy.

So what I did was order two 50uf 600V axial caps from www.justradios.com and a JJ 50x50uf 500V cap can.
I replaced the two huge Sprague Atom 20uf 600V caps with the two 50uf 600V axials. Since the new MIEC German caps were so much smaller than the Atoms I only needed one of the springy cap clamps for each where the Atoms used 2 per.
I replaced the 30/20/20/20 525V cap can with the JJ 50/50 500V cap can. I could do this because the voltages in those 2 stages of the power supply are 400V and under so I get plenty of safety margin with the 500V can.
So now I have the first two section at 50uf 600V and the last 2 sections at 50uf 500V.
I also replaced the bias caps and the cathode bypass cap on the 12AX7.

My total for parts shipped was less than $50 including a new can clamp and power supply resistors, and I upgraded my cap values without having to cram a big board in there and drill new holes in the chassis. The amp sounds amazing now, super tight and deep low end.

This is was for the SS rectified version of the amp but this should still work for the tube rectified version although you might need to stick with a 20uf 600V cap for the first stage.

Hope this helps someone else looking to upgrade or recap their 2000S and do it without having to spend a ton of money.

[Soundmasterg]

This is was for the SS rectified version of the amp but this should still work for the tube rectified version although you might need to stick with a 20uf 600V cap for the first stage.

Good work on your amp! There are many ways to skin the cat as the saying goes.

The max capacitance following a GZ34 tube rectifier is 60uF, so there is no need to use a 20uF in that position. That said, today's modern GZ34's are not equal to the old ones and likely take some care with cap values or they may fail sooner rather than later. The Ruby GZ34 is the best quality new manufacture one these days btw.

On my 2000S I plan to use some Solen polypropylene caps in most of the places in the amp so I won't have to ever replace them again. The downside to these caps are (1) they are expensive, and (2) they are huge. The 2000S has the room though so when I get around to it I plan to do the work to it. I am hoping to get LMS and performance results for noise, hum, output power, frequency response, etc., for before and after, but it all depends on access to equipment when it comes time to do the work.

Greg

[BassHog]

Greg,

I will tell you that the amp is now dead quiet when it's on. It had a noticeable hum when on before due to the old caps. Now I literally have to play it to make sure it's still on as I can't even tell.

As far as the GZ34's go, good to know that they can handle a higher cap. Since the 2000s has two of them do you know if that changes the max cap value on that first stage at all?

I have been interested in those Solen caps, but I have never used them in any of my recaps or builds. They seem very large and expensive. I guess if you literally never have to change them again it would be worth it. Looks like you can get a 47uf 630V axial cap from them though, that would nicely tighten up the low end on your 2000s

Scott

[Soundmasterg]

As far as the GZ34's go, good to know that they can handle a higher cap. Since the 2000s has two of them do you know if that changes the max cap value on that first stage at all?

Scott

You know I was thinking about that when I posted....if having them in parallel would make a difference with the max cap value or not. I am not sure and would need to critically think about it but I don't have time because I am looking for work.

One of the big benefits for using new caps are the noise and hum reduction that comes with it. Glad your amp is quiet now!

You can get 47uF and 22uF Solen 630V from AES/CE Distribution, but there is another supplier that sells clamps and can mount style Solens with 100uF and 51uF (I think its 51 anyway) 630V. The 100uF is HUGE, and the other one is large too, but like I said, the 2000S has the room. I'll try it on this amp and see how it works. I would love to go all plastic caps but don't know of a replacement for the 250uF in the preamp cathode, yet anyway. My 2000S is still stock electrically and I want to overhaul it but I have several projects ahead of it once I get working again. One of these days!

Greg

[Isaac]

My thought on the dual GZ34s is that the capacitance limitation is likely due to the power-on current surge. As there are two GZ34s, they would share the current load, so could reasonably handle twice the capacitance.

Of course, I could be wrong.