Updating and Future proofing mf2500a and PF 1 preamp

[bcupari]

Hello all,

I will state up front I am not technical whatsoever. I have owned both the MF2500a amp and pf-1 preamp for about 5-6 years. There is much discussion about recapping items this old...ie. 20+ years. I'm 60 now and would like to consider getting these 2 items refreshed and making them my final amp & preamp. I live in Tampa, Fl so shipping them around would be pretty costly. There is an audio repair place here in Tampa called Proaudio that seems to good work. However, I want to be able to tell them based on expert knowledge from this board what I want done so they can quote accordingly. I have heard..leave the signal caps alone, only worry about the power supply ones but then I hear others say they replaced this and that and what an amazing difference. I am not having any issues but do wonder if the performance has slipped or if its my aging ears and I don't want the amp to detonate itself and my speakers.

Please provide some much needed and appreciated guidance.

Thank y'all.

Brian

[admin]

This is a hard call. The PF1 is not just 20+ years old, but now almost 35 years old! And the MF2500 is 26 years old. At this point any cap is going to be prone to failure. I think if you really wanted to bring these units up to spec, you would need to replace the caps or somehow test the ones in place that they are still good. If you put quality caps in them, you are going to be spending a pretty penny. Possibly more than what these units go on the used market. If you really love them and want them to operate for another few decades certainly there is no hard limit on how much to spend. Just be aware you are restoring something for the nostalgia, not necessarily price for performance. Nothing wrong with this, but you need to be aware of what you are spending your money on and what you should expect out of it.

It may be worth just looking at newer CJ units higher up the line. My first CJ unit was a PF2. Really liked the sound, but CJ has made "better" gear since then. But you can't put a specific price on nostalgia.

The only thing I recommend you DON'T do, is to hire somebody to do a refurb and put cheap parts into it. Now your spending money and will be disappointed in the outcome. Do a good restoration or don't do it at all.

[microstrip]

I owned a PF1 very long ago - very decent sounding, although not to the level of the excellent PV10a. As far as I remember the PF1 had exclusively film capacitors, so you have nothing to change in it - being a FET design there is not even the usual electrolytic capacitor needed to filter the tube filament supply. Quality film capacitors are supposed to last for more than fifty years - 10exp6 hours at room temperature with non extreme humidity and the PF1 does not run hot. I do not have experience with the MF2500, just owned the older and heavy MF2300. In my opinion you should replace the bank of electrolytic capacitors with good quality Rubycon capacitors - but we must get them from a reliable source, not fakes from eBay or chinese suppliers. Modern electrolytic capacitors can be of very good quality and are not too expensive - technology has evolved a lot in this field.

A few days ago I read from someone who refurbished an old Krell KRS200 with Rubycom gold and now is very happy with it - for some particular reasons it is till my dream and nightmare amplifiers ...

As referred in the previous post everything depends on how much you can trust in the person doing the refurbishment and his fares!

Signal capacitors are much more expensive and a lot of knowledge is needed to choose what to replace and with what - I would avoid doing it without the close supervision of a local knowledgeable expert.

[Big Dog RJ]

PF-1... wow! That's going way back... to before I even knew anything about what CJ stood for! The MF2500 series is also quite dated back but can still hold strong since there have been many MF2300 refurbs upto spec, and they're still sounding tops!

Excellent advice from the above esteemed members, I would take note closely. Also as Admin mentioned, once you're going to engage in a refurb spend... you might want to consider the overall cost given the age of these units. If cost is not an issue and you really want to keep these two pieces of CJ heritage then by all means sky's the limit!

Also, as pointed out by M-S, when replacing caps or other parts, make sure you don't compromise on anything! Otherwise what's the point? You may not get the exact same parts but there are alternatives available at higher grade and quality. Teflons, Dueland, Mundorf, Nichicon, Rubycon, and other metal film types are available at a fine price. These will alter the overall sound definitely but they won't compromise its performance. I know a few close mates you have replaced aging caps with Duelands and Mundorfs, and they in fact elevated the performance.

**Note** make sure that whatever parts are being replaced, they are of same value / type and sourced from well reputed suppliers, hence no compromises ***

Having said that, you could just keep your gear running till something doesn't work properly and then once and for all replace everything that's required. These units don't just blow up... and I don't think you're hearing is defective either. Heck! I know a few 20yr olds who can't hear for shite... my daughter is one of them! Well that's because when I'm talking to her most of the time she's on her damn phone!!! ET phone home...??? Poops.

On the preamp: main reservoir caps plus signal caps if weak... how to tell? A skilled techie can figure that. Also any resistors and internal wiring, plus check all fuses and replace dirty ones. Also fully check all Input & Output connectors, make sure the SE/RCA connections are good from input to output stages. Pretty much the whole preamp circuit.

On the power amp: all main high current caps, plus signal caps, resistors, switches, all fuses, Inputs and main Outputs. Make sure the mains tranny (transformer) is not humming or making any unwanted noise, diodes need to checked and replaced if needed. Basically the whole power amp section needs to be removed part by part and fully assessed. Any qualified techie can do this, plus CJ circuits are simple enough to go through. Nothing majorly complicated unlike other makes.

Just my 50cts worth, hope that helps. All the best!
Cheers, RJ

[bcupari]

Any good tech recommendations near Tampa, Florida. Proaudio is the only one in tampa that I am aware of...