"refurbishing" a Hafler DH110 Preamp

[Talon]

I took the volume apart apart - two screws held the back half on - and had full access to a very fragile-looking scrubber-type contact that traced an arc on a fat graphite semicircle. I dribbled a bit of L5 on it and worked it, and then re-treated the balance and tone pots. I still need to replace the heat sinks for a couple BJTs, and I'd also like to get the 24 RCA female connections on the back scrubbed clean, but I misplaced my cleaning kit. Figures, because I just found it a few days ago, said "Huh, thats where thats been all these years", and then promptly put it in another box and lost it again.

Question: if I don't get the desired result out of the volume control, and it starts making loud popping noises again, I'll have to replace it. Logic and basic rules of resistance tell me yes, I can get the 100k version of the control (OEM is 50k) and place some resistors in parallel with the volume pot to get the resistance curve cut in half, but I'm positive someone here will have a perfectly good reason why doing so would move the doomsday clock another 10 seconds closer to midnight. Any takers?

 

[Talon]

6 V may be a typo indeed, as the standard value would be 6.3 V. Usual steps are 10 - 16 - 25 - 35 - (40 -) 50 - 63 - (80 - ) 100.

It turned out that it was 6.3v.

 

[Talon]

Deoxit F5 for pots
Forget about the IEC socket.
Up to you if you want to change out all the ecaps.
Buy your parts from Mouser or Digi-key, Nichicon UKA or better for signal paths, UPW for supply filtering.
Search Mouser or Digi-key for TO-92 heatsinks.
only change semis if they fail, go noisy

Your hunch is quite likely to be correct - better not trust dodgy eBay sellers.

Nichicon is good for nonpolars. Otherwise, Panasonics are very good caps as well. Wouldn't be surprised if the standard FM or FC series would already qualify as "low ESR" by the standards of the day, let alone FR.

Take measurements of original caps and see what the voltage rating comes out as if you go with same capacitance and physical size. It's usually a good idea to uprate voltage by 1 step at least. Any bump above 63-100 V (or about 3x sustained voltage) is not likely to be worth it though.

Having bought many thousands of caps over the years from several vendors I can tell you that DigiKey is one
of the best if not THE best for searching out parts. When I buy caps the physical size is foremost. Voltage
at least what the original was and I usually go higher as the caps have been getting smaller. The ripple current
is the determining factor as it relates directly to ESR. Usually I look for max hours at 105° but sometimes 85°
caps are fine. Panasonic FR FT and FC are preferred but I've bought a fair number of Nichicons, Rubycons and
United Chemicons. Try again, it's not hard.

Mouser had some Elna Similic parts you guys may or may not approve of, so I quoted all three of you in the hopes you can tell me if I'm on the wrong path here (especially since none of you recommended Elna, but I was just shopping the numbers as best I could):


RFS-50V102MK9#5

These are the main filter caps. They're 1000uF, 50V, 20%, 85c. They fit the site, average 1985 mA ripple. If I get them, they'll be $4.38 plus shipping.

RFS-50V220MH3#5

These are the filter bypass caps, at 22uF, 50V, 20%, 85c. Site friendly, 130 mA ripple. I'll get into these for 67 cents plus shipping.

If you guys spot anything better please shout out. If there's anything about these that I should be against, please let me know. TIA.

 

[AnthonyA]

My buddy did some work on it..

Change all supply caps.. Use nhg /nippon chemicon /pw nichicon or German variant is fine
Tantalum change to sal rpm vishay or solid tantalum.
Final cap out change to silmic. The best upgrade.
Use normal 60 40 solder wire.

Not a good idea to change others to boutique cap just good quality recap . It will sound overly soft and lack of body. No need change the films.

Hope this info is of some help

Just our experience messing with it

 

[Talon]

My buddy did some work on it..

Change all supply caps.. Use nhg /nippon chemicon /pw nichicon or German variant is fine
Tantalum change to sal rpm vishay or solid tantalum.
Final cap out change to silmic. The best upgrade.
Use normal 60 40 solder wire.

Not a good idea to change others to boutique cap just good quality recap . It will sound overly soft and lack of body. No need change the films.

Hope this info is of some help
Just our experience messing with it

Kind of. I highlighted the stuff that I didn't get. In the first line it looks like you threw a bunch of manufacturers and letter variants together and I have no idea what goes with what. In the second line, I don't know what "sal rpm vishay" is. I also don't get why you're saying replace tantalum with "solid" tantalum.
What is "final cap out"?

 

[AnthonyA]

Nhg panasonic
Nippon chemicon khm. Kmq, sme
Nichicon pw..

Power supply cap choices that's we tried is nice. No need to use boutique . If you use boutique capacitors, it will be clean and loses its body.

There is tantalum input coupling cap. You can change to vishay bc sal rpm{ this is best one) . Or even solid tantalum by kemet or Siemens. If change to others.. The grunt and texture will be gone that what made hafler character interesting.

The last coupling cap out... 10uf I think... Change to silmic.

 

[Talon]

Nhg panasonic
Nippon chemicon khm. Kmq, sme
Nichicon pw..

Power supply cap choices that's we tried is nice. No need to use boutique . If you use boutique capacitors, it will be clean and loses its body.

There is tantalum input coupling cap. You can change to vishay bc sal rpm{ this is best one) . Or even solid tantalum by kemet or Siemens. If change to others.. The grunt and texture will be gone that what made hafler character interesting.

The last coupling cap out... 10uf I think... Change to silmic.

Well that's a bit clearer, thanks.

I studied the cap schedule at length and I couldn't find tantalum caps in there. Were they known by another name back then? I see polypropylene, electrolytic, polycarbonate, low ESR electrolytic, NP electrolytic.

From what I've read, polycarbonate caps are long gone and even the NOS is depleted. What can I use in place of those?