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Another Amp for AR 3's


samberger0357

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David, amps with meters sound always better...

I have not tried this one with my unfinished AR3aImroved´s, but McIntosh C26 & MC2125 rebuild is close to be finished.

C26 rebuild was quite easy. Original GE twistlock´s were id good condition, so there was no need to rebuild them. I replaced less than 10 electrolytic´s and cleaned chassis, knobs, switch contacts and lubed switch mechanisms. Very good condition glass panel was sadly broken during shipment, but I sourced new one from Audio Classics. There was some work as new dust shield was needed. Original was turned to dust like condition.

MC2125 was more troublesome, even it was not bad at all to begin. Recapping was quite straight forward, even replacing two 2,2 uF bipolar caps on input sensitivity terminal needed some disassembly. Main reservoir caps caused biggest trouble. When you look pics 6 and 7 you will understand how caps are mounted. Please note how much patina can be removed with rag and Turtle Wax from chassis that has already been cleaned. Anyway, I first bought 12 000uF Nippon  Chemi-Con caps to replace the original 10 000 uF Mepco´s. But I was not aware that high post terminals were needed and Chemi-Cons did have low post ones. I first tried to find reliable way to isolate voltage rails from chassis... but could not find suitable spacers and reliable insulators... So I decided to buy new Cornell Dubilier caps of twice the original capacity and correct high post terminals, luckily the original bridge rectifier has not failed due increased peak load to them. CDE´s were actually only caps available that were suitable for this amplifier. If you look at the pic, manufacturing date is 0953 and these were sourced from Mouser, so it might be right time to rebuild amplifiers that do need caps like these. After all these caps are not too expensive now, and I would not bee too keen to use NOS electrolytic´s for rebuilding amp that is going to be used.

There is still something fishy in temperature compensating circuity in one MC2125 channel, but it is working otherwise well now. I am not ready to say too much about sound quality of this combo, but it has proven to be nice combo to work with. Amplifiers have been constructed quite well even there are some safety issues that are hard to understand. Say unused power transformer primary taps have been soldered to uninsulated tag board close to main amplifier PCB, so you can quite easily touch mains voltage when measuring voltages on the PCB. 

Very nice amplifiers...

Kimmo

PS in the last pic. Mr. & Mrs. Duck waiting McIntosh gear to be finished...

 

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I admire your fortitude in restoring the Mac C-26 and MC2125 in far-away Finland; living just a few hours' drive from the McIntosh factory (and the great Audio Classics), I've hit the Wall Of Frustration waiting for parts more than once. ^_^

I've never owned the MC2125, but I did have a new C26 preamplifier back in the '70s, and it was really nice. I mated it with a new MC2205, and that was the setup with my very first pair of AR-9 speakers.

McIntosh featured the C28 as their premier preamp at that time, but I enjoyed using the continuously variable loudness control on the C26; especially at lower volume levels to maintain the LF balance with the AR-9.

Great work, Kimmo - the chrome & glass look like new - congratulations on a fine restoration!

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Thank you for your kind worlds ar_pro. I guess if you have used MC2205 you will be familiar to MC2125... they do use same topology. 2 dB higher volume of MC2205  is gathered by adding third pair of output devices as well scaling transformers and PSU for this purpose. Output transformer taps are slightly different, but this is usually irrelevant unless you use amp in bridged mono configuration. As far as I know MC2205 outsold MC2125 by quite margin, so it must have been quite keenly priced in the late 70´s. For me 29,5 kg weight was reason for choosing 2125... amps over 30 kg are not for me anymore,  unless...

I was actually looking for C28, but when I saw decent C26 at ebay... I though, what a heck should I try this one? I found later that this was not bad decision at all. If you look how many switches and other functions are in the line section, it is small wonder how wonderfully this little gem designed in 1967 does perform. Phase switch designed to reverse phase of miss phased speakers is oddity, that you are unlikely to find elsewhere. 

McIntosh was not distributed here until late 80´s or early 90´s, so sourcing these is easier from your side of pond. This makes things at least more expensive. Tax and duty has to be paid for 2nd hand items too. Freight of goods is usually expensive too. Due broken C26 glass I decided to buy MC2125 from Audio Classics. Steve Rowell was very helpful and he even sourced new glass for C26... he actually said he would not place C26 glass same carton with MC2125 to save money... this was good advice. 

It seems that I do not get frustrated too often for waiting parts, as I do have so many unfinished projects that it is easy to start doing something else. 3 small Citation 11 inductors on my desk have been waiting for rewind at least 3 years. This may happen this year or later... I usually get upset and say too many four letter worlds due to my limited soldering skills or lack of light while soldering. I am lucky to have so wonderful wife as she always does remind me that this is my hobby... relax, do not get upset... She even helps me quite often when I need 3rd or 4th arm to hold something when soldering,,,

It is also nice to have so many friends here. We may disagree certain issues, but I believe we do have quite much common too...

Kimmo

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Steve Rowell is a terrific guy, and his knowledge of vintage McIntosh equipment is extensive. The last time that my wife and I were at Audio Classics, he called and arranged a McIntosh factory tour, just for the two of us.

You're 100% correct about the price of the MC2205; at an unusual discount, it was just a bit more expensive than the MC2125 - I believe I paid about $1,000 in 1979, as the amp was nearing the end of its production run. With the C26, it was a great match for the AR-9.

If you haven't seen it, here's a nice article by Roger Russell, the designer of the C26: http://www.roger-russell.com/c26pg.htm

 

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Hi, friday evening and vacation :)

I have a chance to get a yammie m-4 and a crown 202 for about 460€. For now I agreed and then had to decline as I couldn't take of yesterday too meet halfways. "I have the C-4 and probably diy buffers, phonostages and input selectors that are far better than the C-4. One idea I have is to archieve the innards of the pre and put in my own stuff." The C-4 have its virtuses - I will rather fix it and keep it as is... But the real question is - should I take precious time of to hunt these down? I decided not. The price was a bit high considering a half days driving just to collect them. I rather get my AR-3's working first.

I'll add that everything is better than my C-4 right now. As it was playing for a few hours suddenly one channel broke down with even more distortion as time went by. I wasted a good number of hours trying to find where I made an mistake in my newly assembled speaker... At last I switched to my old prebuffer and sound was back- undistorted. I opened the C4 up an found more than a few joints that seems needing an resolder. I'll put this aside for now until the ar3's are online. Looking inside the C4 was a joy - thy don't build that way anymore. HiFi of the heydays :D

An Austrian company sold it as good working on ebay :D Be aware...

Regards

 

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  • 2 months later...
On 17.2.2016 at 9:31 PM, Sonnar said:

Sometimes I drive my AR 3's second pair ( pine plywood ) with a 1962 Allied-Knight KA-25 , a little and cheap 10 watts per channel integrated, with 6BM8 tubes. This could be an heresy, only ten watts for an AR 3! But at low listening levels and with some chamber or baroque music , or string quartets, the joy of listening is superlative. 

I found less than month ago this nice HH Scott 299-D Stereomaster (before switch to lower grade output transformers from 233) with multi voltage power transformer. Construction is far behind Quad or Leak standard, but it is from same era than your KA-25... maybe a bit more upmarket design. However condition of this amp is quite good, even I managed to wash some chassis markings off when removing 50 years of patina. Chassis pics are before pics and front plate pics are after washing grime off. 

This may be little off topic, but it may help other vintage enthusiast´s too. However, I have had problem to find suitable replacement for RCA- jacks for this amp and also for several other 60´s to 70´s amps. Switchcraft BPJF03X is small enough, but with close original jack spacing there is hardly enough space to tighten nut with long socket.  http://www.mouser.com/ds/2/393/bpjf_x_series_cd-479449.pdf

Keystone 568 looks also small enough. But I can not figure how this rivet termination works... can enyone explain this to me? Quality might not be top notch as data sheet list it as rivet style PHOTO jack...http://www.mouser.com/ds/2/215/p70-478290.pdf

Good alternatives seems to be too few... most often I have tried to clean original jacks as well as possible. However some jacks in this Scott are so rusty that replacement is only option. And I do not want to ruin original appearance of this amp. 

Does anyone have any good ideas for phono jack replecements.

Kimmo

 

 

 

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Hi Kimmo, I can't really help you with your specific request for sources of new jacks, but it looks to me like your RCA jacks are in pretty good shape already. Just a heads-up here - - - before you even think of hooking up this amp to vintage AR-s with 12" woofers, be sure to disconnect the yellow and green wires from the 16-ohm taps on the rear of the amplifier and reconnect them to the 4-ohm screw taps. Nice looking amp, good luck with it.  

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Nice catch, Kimmo ! The Stereomaster 299 was one of the best integrated amps of its time, my Knight and Eico ST 40 were cheap kits , but the Scott had superior building quality. In order to preservate its original appearance, if not damaged , try again to clean the jacks , brush away the rust and then use some chemical product to restore conductivity. If it doesn't work , I prefer to give a chance to an expert professional technician . My Knight and Eico were refurbished by an excellent technician with NOS Westinghouse 7591 output tubes, modern Electro Harmonic 6BM8 tubes and german-made capacitors. Not original, ok , but still working. Best regards , Adriano

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Problem with maybe 5 pcs of jacks is that there is so much rust that rubbing with toothbrush and toothpaste was not enough to remove rust. It might be possible to remove rust with wet sanding paper, but how to apply new plating and what kind of chemical product is needed for new plating? It would be nice get advice how to restore jacks such a way that replacement can be avoided. 

This amp is obviously very low mileage unit... I suppose that only one smooth plate Telefunken has been replaced with ladder anode Mullard and one original 7591 has obviously passed best before date... however I have now reformed original caps but not tried how this amp is working... I suppose I will find suitable replacement tube set as I finished my 25 years long tube distribution part time job last year and I have enough vintage tubes for rest of my life.

One peculiar feature of this amp is center channel output... output transformers are grounded from 4 ohm taps and one 16 ohm tap and one 0 ohm tap is used to make third channel monophonic output from power section.

Kimmo

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Try this one , CRC rust remover. I 've used it on a very early Soundcraftsmen PE-2217 Preamp-equalizer with excellent results. My father used it on his norwegian Fjord motor boat , and I use it on my vintage electric equipments. Maybe strange but it works. 

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On 9/19/2016 at 4:37 PM, Sonnar said:

ry this one , CRC rust remover.

Just a caution: The larger picture of rust CONVERTER would not be good. Rustoleum sells a similar product on this side of the pond and as the label says it convert rust to a "tough black primer".

Kimmo, try the Scott 299 thread on audiokarma (linked in the next post). AKer Craig "NOSvalves" is an expert on rebuilding these and should be able to point you in the right direction. Here's his web site http://www.nosvalves.com/-Kent

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On 9/19/2016 at 0:31 PM, iso said:

I found less than month ago this nice HH Scott 299-D Stereomaster

A related question: 

I was fortunate to have a friend give me a Scott 299A that had sat in a closet for decades. With some help from the folks over on AK and my tech friend, I replaced "most" of the electrolytics, some caps and installed a bridge rectifier. http://audiokarma.org/forums/index.php?threads/scott-299a-2nd-version-rebuild.473624/page-2

Love the vintage tube amp but is its 17wpc too weenie to drive my AR-3a's? I was using an AR receiver (60 wpc) which seemed like enough but that's out for service. Right now I have an Advent 300 in there, which has a power output similar to the Scott, so I'm thinking the Scott may be OK. But respected members here tell me the 3a likes massive amounts of power.

Input?

Here's a photo.

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On 21.9.2016 at 7:52 PM, JKent said:

Just a caution: The larger picture of rust CONVERTER would not be good. Rustoleum sells a similar product on this side of the pond and as the label says it convert rust to a "tough black primer".

Kimmo, try the Scott 299 thread on audiokarma (linked in the next post). AKer Craig "NOSvalves" is an expert on rebuilding these and should be able to point you in the right direction. Here's his web site http://www.nosvalves.com/-Kent

 

Adriano and Kent

 

I believe phosphoric acid is most common base for rust removal/converter products. It turns iron oxide to more stable iron phosphate... it is good when it is impossible to remove rust before painting.  I suppose downside is that iron phosphate is not too good conductor. When I used vinegar for rust removal it did leave similar black colored residue on oxidized screws... so it might also have similar downsides too.

 

I am a bit jealous how you fellow members on your side of pond seem to find nice items like your Scott 299-A for free or pennies. Your recap story was very nice... I have only checked that 100nF coupling caps to output tubes seems not be too leaky, at least when the amp is "cold". However I have some vintage  ERO 1801 and 1813 series MKT caps I bought in early 80`s. These might be nice for this one, but 22nF and 27nF values might be needed if these turn to be leaky. ERO´s are looking so gorgeous that they must be good. I may post pics later for these.

 

My 299-D does not have wooden sleeve, so I must make one... can you add pics about profile or contour of front opening of the case and let me know how chassis is attached to the case.

 

ra.ra

 

Jacks are actually looking very good on the pics. Unfortunately it seems that replacement is only real world solution unless amp turns out to be compete turkey. I will post what kind of reply I will get from Mouser for possible replacements... but If anyone here does have any good ideas for replacements, let me know.

Kimmo

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Two years ago I stopped by a garage sale and purchased some vintage University speakers and ask if they had any thing else. The lady said there was a old radio in the basement, and it turned out to be this Scott 299C which she threw in with the speakers. 

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The RCA jacks make Kimmo's look good.  That basement must of been damp. I am interested to find out if he comes up with replacements. I doubt if they can be salvaged.

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On 9/19/2016 at 3:22 PM, iso said:

I have now reformed original caps but not tried how this amp is working

I found that most of the original caps (AND the original tubes) in mine were still good, although I did replace 3 of the big "cans" and all of the electrolytics and paper caps that I could reach ;)

I was told that the old selenium bias bridge is unreliable and to replace it with a modern bridge rectifier. That change also necessitates changing the downstream 10 ohm 2 watt resistor. There's a point to check the voltage and with a bit of experimenting a 47 ohm 3w worked just right. YMMV.

Kimmo--back to your RCA jacks. Craig over on AK said he makes new acrylic plates to mount the new jacks and he spreads them out a bit to allow more room http://audiokarma.org/forums/index.php?threads/scott-299a-2nd-version-rebuild.473624/page-4

Kent

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I'd attack the rust the old-fashioned way, with wire brush heads on a Dremel tool and a big tank of compressed air. DeOxit will clean up any traces left. Be sure to follow up with a protector, because the rust will have eaten away any original coatings (steel chassis would originally have been clear lacquered).

Single RCA jacks are readily available. A gang of three, you'd have to make yourself. But as long as all your old ones have is surface rust and the center contact still has its springiness, cleaning shouldn't be a problem. 

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Just acquired a beautifully restored Fisher 400 and couldn't wait to use it with a more efficient pair of speakers so hooked it up to the 3's. What a glorious sound. Again, small room, reasonable listening levels, mostly jazz and acoustic music, but wow. Yes, my 175 watt Yamaha M4 sounds great with them, hell so does my 90 watt Sherwood 8900A receiver. But other then perhaps a small lacking in overall oomph, there is something so special about using a period correct Fisher tube amp with the 3's. 

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2 hours ago, samberger0357 said:

Just acquired a beautifully restored Fisher 400

Nice! My tech prefers vintage Fisher over vintage Scott but I think all the old stuff is pretty cool.

To follow up on an earlier comment, it seems the "center channel" was fairly common during this era. Certainly both the Fisher and the Scott had it. I wonder if it was part of the transition from mono to stereo. Mono hi-fi enthusiasts who needed a new amp could buy one of these and not have to worry about buying another speaker, new turntable, tuner, reel-to-reel tape deck.......

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5 minutes ago, JKent said:

Nice! My tech prefers vintage Fisher over vintage Scott but I think all the old stuff is pretty cool.

To follow up on an earlier comment, it seems the "center channel" was fairly common during this era. Certainly both the Fisher and the Scott had it. I wonder if it was part of the transition from mono to stereo. Mono hi-fi enthusiasts who needed a new amp could buy one of these and not have to worry about buying another speaker, new turntable, tuner, reel-to-reel tape deck.......

I had the impeccable timing of obtaining it on a 100 degree day here in NoCal, but I don't care. And I don't care if it's "not enough power" for the 3's, because it's sounds friggin' great to these ears. Tubes and 3's go together like scotch and soda. Now, if I had a larger room then my little band box it might be a different proposition, but the 400 gives me all the power and dynamics I need in my abode.  Here's the distance from my listening chair. 

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In the early days of stereo, it was common for poorly mic'd recordings to have a "hole" in the center. Blending signals and feeding them to a "derived center" filled that hole. There were a very few recordings made that actually used phasing to produce a deliberate center, but you could search your local used record dealer for weeks before you found one. Mostly, what you get from the center is a thin signal that can pass for ambience when the third speaker is placed behind the listener (the Hafler effect).

If I had my hands on one of these amps and wasn't all that hung up on keeping it original, I'd repurpose one of the three Mag input jack pairs as a pre out. Then I could send a signal to a beefier power amp and biamp.

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I still have difficulty understanding, at least audibly, why, in a a specific situation, with the AR3's,  one couldn't get away with with a 20-30 watt tube amp and live happily ever after. Unless you might want concert hall volumes(which I don't) and wall shattering bass(which I don't), or listen in a very large room(which I don't) I simply don't find much difference between my 170 watt Yamaha M4 amp, and my 28 Fisher 400, at least at lower, more reasonable levels. I can get the Fisher plenty loud, and it provides a certain quality that I love that the M4, or any other solid state that I've tried for that matter, I don't miss anything that I have when listening to a much more powerful solid state amp. I know all about big power supposedly "opening up" the 3's because they're so hard to drive, but I just don't hear it. There must be others here that feels similar.  Everybody's situation is certainly different, but dismissing out of hand a 25-30 watt amp for use with the 3's I believe is something that shouldn't be done automatically. 

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You certainly could, if you have a relatively small listening space (think NYC apartment living room) and don't play your music at very loud levels (the old rule used to be that you should be able to carry on a conversation with another person in the room without having to raise your voices to be heard over the music). That's what AR had in mind when they set the min recommended power for the AR3 at 20wpc.

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