Stax SRM-600 recap

[jsts]

Folks, I replaced all the electrolytic capacitors in my SRM-600.

I can't say for sure if this has happened before, but this (photo) capacitor at 10V 4700uF is heating up. Not very much, around 55C. The headphones aren't plugged in.

Can you tell me if this capacitor is in normal operation? Does it have to warm up?

My SRM-600 for 230V voltage.

First, I supplied a cheap Jamicon TKR472M1AJ26 capacitor. It was heating up.Then I decided to place EEUFR1A472L Panasonic Low ESR capacitor. However, it's warming up, too.

I checked the diodes next to it - they're not broke. On the cap about 7V.

Any other caps running cold. Only 4700uF/10V running warm. I double-checked all capacitors parameters and they match (or exceed) the original:

 

Original:
ELNA LAH400V221MS36 220uF 400V 25х45mm/10mm <--- Rated ripple current (RRC Arms) = 0.87
Replacement:
TDK/EPCOS B43642B9227M0 220uF 400V 25x35mm/10mm <--- RRC = 1.03 & ESR at 100 Hz = 460 & Impedance = 680 

Original:
ELNA RJ4 4700uF 10V 12.5x25mm/5.0mm <--- RRC = 1250 & ESR = 0.11
Replacement:
Panasonic EEUFR1A472L 4700uF 10V 12.5x30mm/5.0mm <--- RRC = 3630 & Impedance = 0.013

Original:
SANYO 35ME470HC 470uF 35V 10х16mm/5.0mm (S.E.8N Black 85°C Standard series) <--- RRC = 585
Replacement:
TDK/EPCOS B41888C7477M000 470uF 35V 10х20mm/5.0mm (B41888C7477M000) <--- RRC = 1500 & ESR at 10 kHz = 0.050 & Impedance = 0.046 

Original:
ELNA RC3-16V470MF0 47uF 16V 85°C 6.3x5.0mm/2.5mm (RC3 F0 Blue 85°C) <--- RRC at 85°C = 70
Replacement:
HITANO E5R 47uF 25V 105°C 6.3x5.0mm/2.5mm <--- RRC at 105°C = 60

Original:
ELNA RC3-50V100MF0 10uF 50V 85°C 6.3x5.0mm/2.5mm (RC3 F0 Blue 85°C) <--- RRC at 85°C = 40
Replacement:
ELZET CD50H 22uF 50V 105°C 6.3x5.0mm/2.5mm <--- RRC at 105°C = 40


Before the replacement, I did not check if the 4700uF/10V had been warmed. This could be his normal operating condition.

It is simply not clear to me which components of the circuit can affect it: from the transformer comes two BLU-wires at 6.3V AC current, then there are two diodes in parallel converting to DC current, and then there is a 4700uF/10V capacitor, which receives these 6.3VDC. There is simply nothing to break.

Any suggestion?

Edited November 24 by jsts
Large size of attachments.

[kevin gilmore]

so you did not get the information you wanted over there, and now you come here. nice.

from pictures elsewhere, the transformer winding is blue-black-blue and is 12.6v center tap, 2 diodes to capacitor full wave bridge.

This is the filament supply and has high current ripple. The cap you have chosen is completely wrong for the job. 

All the original caps were chosen for a reason, if they are not dead then you should not be replacing them.

And you should be careful touching that cap with the power on, as its sitting at -350v.

[jsts]

Mr. Gilmore, thank you for your attendance, it is very important to me.

It seemed to me that Head Case has more DIY-ers and to check with other owners if the capacitor warms up, there are more chances.

Then I'll go over the circuit again and try to understand the exact difference between the original capacitors and the replaced ones.

 

30 minutes ago, kevin gilmore said:

And you should be careful touching that cap with the power on, as its sitting at -350v.

Thank you so much, I didn't think about it. I will try to be more careful and if I survive, I will continue to write about my adventures in the STAX world :). I just listened to music for 10 years and was not interested in anything else. And then I read your articles, other Audio Wizards articles and decided to improve my beloved amplifier.
 

[kevin gilmore]

should be 12.6 vac rms measured blue to blue

should be 8.5 vdc on that cap.

should be 6.3 vdc after the regulators measured at the tube filaments.

everything referenced to -350V

 

[spritzer]

Why are you changing those caps?  Any of the claims out there that this cap sound like this and this one is good for this spot... it is all bullshit.  This is a niche circuit so special care has to be taken when picking caps for that. 

[jsts]

17 hours ago, kevin gilmore said:

should be 12.6 vac rms measured blue to blue

should be 8.5 vdc on that cap.

should be 6.3 vdc after the regulators measured at the tube filaments.

everything referenced to -350V

 

That' s great information. I'll double-check everything. Thank you.

 

16 hours ago, spritzer said:

Why are you changing those caps?  Any of the claims out there that this cap sound like this and this one is good for this spot... it is all bullshit.  This is a niche circuit so special care has to be taken when picking caps for that. 

Hello, spritzer! 🙂 My SRM-600 is 10 years old and many forum members recommend changing all capacitors after 10 years of amplifier operation. Well, I have replaced...

[jsts]

I've measured all voltages:

- measured blue to blue = 12.3VAC
- measured on the capacitor 4700uF/10V = 6.8VDC
- measured at the tube filaments after the regulators = 6.15VDC
- measured everything referenced to black -347V

 

Two diodes is 8B 21DQ04. I dropped them off and checked them out. They are guaranteed to work (they pass in one direction and infinity in the other).

 

Circuit:

All that remains is to return the old capacitor and see if it will warm up. If so, that's his normal state.

Edited November 24 by jsts

[kevin gilmore]

any ac voltage on the filament? likely the regulators are on the verge of dropping out of regulation.

is your 230v about 3% low?

[jsts]

Clarifications:

- It turns out that all the wings in the transformer are connected. Thus, it works at 240V.

 

 

- The voltage in the power outlet is 230±5V (the input voltage fluctuates within 2-3%).
- there is no AC-voltage on the tubes.

 

Up-to-date tube power supply circuit:

 

I can rewire the power supply to 220V.

Edited November 24 by jsts

[jsts]

Addendum:

Today (sunday evening), the power outlet has a 240VАС.

I've again measured all voltages:

- measured first blue to black (transformer) = 6.43VAC
- measured second blue to black (transformer) = 6.43VAC
- measured blue to blue = 12.86VAC
- measured on the capacitor 4700uF/10V = 6.83VDC
- measured at the tube filaments after the regulators = 6.15VDC
 

That is, the diodes give stable 6.8VDC to 6.83VDC, and voltage regulators give stable 6.14 to 6.15VDC. That seems to be the design.

[jsts]

Up-to-date tube power supply circuit (around voltage regulator):

Edited November 24 by jsts

[jsts]

I'm still alive 🙂 and finally I found an oscilloscope.

Up-to-date tube power supply circuit:

 

I'm looking at a 4700µf/10V capacitor (where I previously measured 6.83 volts with a multimeter):

The total pulsation is about 2 volts. Voltage (real) is 7.62 volts.

I look at the leads to the tubes (where I previously measured 6.15 volts with a multimeter):

That's 6.33 volts, all right.

I draw a conclusion that the capacitor 4700µf/10V heating is a working design and so conceived by the manufacturer.

I will try to replace it on Panasonic EEUFS1A752L 7500µf/10V.

Edited November 24 by jsts

[jsts]

Finished the experiment.

First put a Panasonic EEUFS1C512L 16V/5100μF capacitor. It also warms up, about 55C. That is, the increase in voltage rating has not changed the situation.

Then I put a Panasonic EEUFS1A752L 10V/7500μF. It is warmed up, but less, about 49C. That is, a 60% increase in capacitance rating led to a 10% decrease in temperature.

Left 10V/7500μF, can no longer improve, 20000μF nowhere to place.