Questions on removing electrolytic caps

[rusty-jade]

I recently completed building my stereomour.  I then upgraded the parafeed and coupling caps with Clarity MR series caps. Next I removed the volume and selector switch connections and turned it into a power amp, using my 30 year old Cary SLP-30 preamp.  I was astounded by how good the sound is, better than a previous 2A3/300B amp I owned.  I am planning to do some further upgrades, including using the Triad CX-7 chokes and replacing the electrolytic caps.  I have some questions on the latter, and please pardon my ignorance.  In one of the threads, PJ states:
"The output tube cathode bypass capacitor (which is on the PSU board) can by bypassed with a film cap across the cathode resistor, T1-T11 and T5-T15. To completely replace the electrolytic, simply remove the wires from T1 and T5 to the PSU board "K" connections.
The best place for film bypass capacitors in the power supply would be from the B+ outputs on the PC board, to the nearby cathode resistors at T1 and T5. An extra hole is provided on the PC board for this."

-However, when I look at my Stereomour, the corresponding terminals seem to be T16-T6 and T20-T10.
Am I missing something here or did the numbering change after PJ's post?

-In addition to the two aforementioned 220uf 250v cathode bypass caps, there are still two more 220 uf caps, that are in parallel ( based on the schematic diagram) to the 100uf power caps?  What should happen to these two?

- Regarding replacing the 100 uf power supply caps with film caps,  I assume the B+ outputs mentioned in the above quote is the HV+ holes and again T1 and T5 should be T16 and T20? 
- When this is done, do the 100 uf caps have to be disconnected/ removed?

Any advice will be greatly appreciated.     

[Jim R.]

RJ,

If you're going to use the triad ps chokes, then you can remove the 100 uf 450 v caps on the ps board and wire in some 30 uF film caps of sufficient voltage rating.  I'm planning on this myself and bought a pair of mundorf m-tube 30 uF caps for this purpose.  You are also correct that these are separate from the cathode bypass caps -- those can be anything from 47 uF and up and would be most effective if the leads to the ps board cathode bypass caps are removed as PJ states.  As for the first 250 uF electrolytics, probably best to just leave them -- they are needed for the voltage doubler circuit and are the first caps in the ps circuit.

Of course this is also assuming that you plan to use the triad c7x chokes with the requisite 270 ohm dc resistance, and that you wire these in place of the two 270 ohm resistors on the ps board.

Anyway, here's the summary:

1) remove the cathode bypass wires to the ps board (and optionally the electrolytic cathode bypass caps (220 uF 250v), the 2 270 ohm resistors on the ps board, and the 100 uF electrolytics (not totally necessary, but probably recommended.)

2) replace the 100 uf caps on the ps board with film caps of 27 uF or greater (using the extra holes in the ps board), and install a cathode bypass cap of 47 uF/100v or greater film cap directly to the terminals of each power tube (sorry, don't have terminal numbers in front of me), and finally wire the 2 triad chokes in place of the 270 ohm resistors.

That should be a significant upgrade, and one I'm planning on myself.

Hope this helps,

Jim

[rusty-jade]

Thanks Jim.  I intend to replace both pairs of the 1200 and 360 ohm resistors on the PS Board with the Triad chokes ( when they arrive!).  And thanks also for your suggestions on the replacement of the 100uf and 220uf electrolytics. They reinforce my understanding of what I plan to do.

[Jim R.]

Oh, good point -- I plan on building my amp for 2a3 only so substituted a single 270 ohm resistor for the 360/1200 combination.  The above pertains to 2a3 only and if you wanted to use 45s, you'd either have to add some series resistance to the chokes to bring them up to 360 ohms, or find another suitable choke with a 360 ohm dc resistance.

-- Jim

[Paul Joppa]

...
-However, when I look at my Stereomour, the corresponding terminals seem to be T16-T6 and T20-T10.
Am I missing something here or did the numbering change after PJ's post?...

You are correct, and my post was wrong. I will try to find it and edit it. I erroneously remembered the numbering scheme, which was bottom line first, then the top line. My error, my apologies. Guess I was in  a hurry that day.

[jimiclow]

Oh, good point -- I plan on building my amp for 2a3 only so substituted a single 270 ohm resistor for the 360/1200 combination.  The above pertains to 2a3 only and if you wanted to use 45s, you'd either have to add some series resistance to the chokes to bring them up to 360 ohms, or find another suitable choke with a 360 ohm dc resistance.

-- Jim

You only need the 1.2K resistors for 45 operation.

[rusty-jade]

Thanks for all your help.
I have built the Stereomour as a 2A3 amp but I may, in future, eventually try it as a 45 amp, when I will need to add a 900 ohm resistor in series to the Triad choke plus other changes as stipulated in the Manual.  My only hesistation is my speakers are 98db sensitivity ( Tekton Lores) so it could be just on the borderline for the 45 tube as far as sensitivity is concerned.  I wonder what speaker sensitivity have other members used for the Stereomur as a 45 amp?

[Jim R.]

Jimicloe,

Thanks for pointing that out -- forgot which resistor was removed for 45 operation.

-- Jim

[Grainger49]

   .  .  .   My only hesistation is my speakers are 98db sensitivity so it could be just on the borderline for the 45 tube as far as sensitivity is concerned.  .  .  .   

We had Paully's 45 amp here a month or so ago.  I have 94dBW speakers in a 27'X13'X8' room.  Paully listens at lower volume levels than I do.  Hooked to my speakers with my powered sub (crossed who knows where) I put on a Japanese Taiko LP and turned it up, way up! 

I was shaking the room and my listening chair!  I'm surprised I didn't get acoustic feedback to my TT.  It could be heard all over the house.  I had to be playing 10dB louder than I usually listen.  Taiko drums are large and include a lot of low frequency information.  Still my speakers were rocking the whole house with the 1.75WPC.

[Jim R.]

And I plan to use my sr-45s with my Blumenstein Nagas -- roughly 88-90 dB.  Room is small though.

-- Jim

[jimiclow]

Thanks for all your help.
I have built the Stereomour as a 2A3 amp but I may, in future, eventually try it as a 45 amp, when I will need to add a 900 ohm resistor in series to the Triad choke plus other changes as stipulated in the Manual.  My only hesistation is my speakers are 98db sensitivity ( Tekton Lores) so it could be just on the borderline for the 45 tube as far as sensitivity is concerned.  I wonder what speaker sensitivity have other members used for the Stereomur as a 45 amp?

Hi Rusty,
I built my Stereomour as a 45 amp, powering a Hoyt-Bedford (Omega) Type I full range (97db) and they get pretty loud. I have a JBL sub though.
If you're planning to try 45's, I suggest using no less than 1.3k resistor in addition to the choke (270 ohms). The stock 1.2ks are running the tubes at 300V p-k which I think is pushing the tubes hard. Even EML suggests running their tubes between 250-275. For now, I'm running the amp thru a variac at around 275-280 volts. I will eventually change the resistor to 1.8k. Partly to blame also is my line voltage which runs around 123 volts most of the time.
Can you show us a picture on how you modify your amp with the choke?
Thanks.

[rusty-jade]

Hi Jim R,

RE: the Mundorf M-tube caps ( 30uf), are you planning to install these directly on the PC Board?  I looked at the specs for them and its width is 35mm, with the leads 30 mm apart, but the diameter of the stock 100uf electrolytic caps is only 25mm, with very little extra room on the PC board. 

[Jim R.]

No, I wasn't going to try to install them on the existing ps board -- though I haven't looked at the board in a while, so maybe when the resistors and cathode bypass electrolytic are removed, there may be room to epoxy them onto the board and run some short leads to the old 100 uf cap holes, or the extra holes on the board for the off-board caps.  And this also assumes that the ps chokes will be mounted elsewhere and leads run to the resistor pads on the ps board.

I've also given some consideration to building a whole new ps board out of g-10 or some thin birch plywood and hardwirig the few components, but a final verdict on all this will have to wait until I have the stereomour on the bench again when I'm ready to do the wiring.

I never thought the leads would fit, so sorry for not mentioning that.

-- Jim

[Grainger49]

R-J,

Often upgrade parts don't fit where stock parts did.  That was one of the reasons for my posting the picture that I linked in my last PM. 

I guess good parts are just large.  Well, I'm not guessing.  In the case of capacitors the better sounding ones are a thicker dielectric.  Electrolytic caps are very compact for a given voltage rating and capacitance value.  Again, compare the 1400uF 450V electrolytic with the similarly sized 10uF 660V AC "Oiler."

[earwaxxer]

Here is the 'mother of all caps' to put Grangers statement into perspective. It the Duelund Cast 300uf. Weighs in at over 25 kilos EACH! Dont even ask what it costs!