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New to me Fisher 400 - first assessment

Patrice B

Patrice B

Super Member
Hello,

Long time I didn’t posted at AK, being more active in guitar/bass tube amps restoration since 6-7 years!

Anyway, I couldn’t help myself when I saw this Fisher 400 with wood case and even original box on FB Marketplace.
As the seller said it wasn’t working (fuse blowing), I took a chance… for 450 CAD! He originally bought it from the original owner in the States back around 10 years ago. I think it was still powering on back then.

As you’ll see, that thing is filthy and was probably in a wet environment in its life.

Anyway, the four 7868 tests ok with no shorts on (albeit one is weaker that its siblings) my Precision 612 tester. No other tubes tested at the moment. They look to be the original ones: Telefunken and some USA ones in the MPX.

A quick ohm test showed that the OPT’s are healthy so I suspect something in the power supply, probably the electrolytics. The bridge looks to be a Silicon one as the receiver is a later revision (didn’t found any SN!) as seen by the three 6AU6’s in the tuner section.

My plan is:

- replace every electrolytic, including the 1uf in the MPX section;
- unless someone tells me that the ERO caps are ok, replacing the caps only in the pre, power and phono section.

Obviously, a cleaning is also in the plan, including Deoxiting the switches and tube sockets.

Patrice

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gadget73 said:
if thats as-found with no cleaning, honestly I wouldn't consider this to be any worse than just dusty. I've certainly seen worse.
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« As-bought » would be more appropriate but yes, you are right!

BTW, thinking about going discrete for the electrolytics, lots of space underneath and I have a big stock of terminal strips.

Missing knob brights: when I got my X-100-2 and FM-200B several years ago, I’ve replaced every knob caps with silver ones (sacrilege) as there were only 3 remaining. Guess where those three will be used now?
 
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I bought my 800c in 2017 and changed out all the electrolytic capacitors except the can capacitors. Someone had installed orange drop coupling capacitors. It had JJ 7591’s when I got it , they lasted about 1 month then 1 red plated. Switched to new production Tung sols reset the bias and they worked until this February(9 years almost daily.)Red plated a 7591. Replaced all the can caps with Hayseed Hamfest replacements back in business. The original can capacitors were way off but still played. It’s past time at 60 years. Avery Fisher equipment sounds as good as almost anything in production today and great build quality and restorable.
Good looking 400.
 
Freddie73 said:
I bought my 800c in 2017 and changed out all the electrolytic capacitors except the can capacitors. Someone had installed orange drop coupling capacitors. It had JJ 7591’s when I got it , they lasted about 1 month then 1 red plated. Switched to new production Tung sols reset the bias and they worked until this February(9 years almost daily.)Red plated a 7591. Replaced all the can caps with Hayseed Hamfest replacements back in business. The original can capacitors were way off but still played. It’s past time at 60 years. Avery Fisher equipment sounds as good as almost anything in production today and great build quality and restorable.
Good looking 400.
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Nothing done yet but thanks for your encouragement!

I’ll use old stock 7868, if possible the set that came with the unit. I’ll do it all under the hood with discrete electrolytics. Now, just missing the initial motivation :biggrin: !
 
I restored a 400 several years ago, it is a nice sounding unit! I used EH 7868 tubes as at the time Nos 7868's were a bit pricy but looking back I should have went NOS......
 
To test the power transformer, I remove all tubes (and put a brand new fuse, obviously) and try to power on, right?
 
Nice receiver, I partially restored mine years ago including the diode bridge in the MPX unit that someone butchered, luckily that was the only work done to it. I still need to finish replacing the above chassis lytics. Though the unit performs well I don't like how warm the voltage doubling cap gets so I haven't been using it much. When complete you will have a beautiful receiver.
 
Ok, some progress, yes I am slow!

First power on, no output tubes, 3A slow blow fuse: fuse died!

Second power on, HV and Bias supply unsoldered, no output tubes, 3A fuse survived. I got 163 VAC measuring the red and red/yellow secondary. Is that ok? My expertise really end there but I assume that the HV rectified then going to the voltage doubler would give me some correct DC voltage, right? Power tranny is healthy, what do you think?

Third power on, HV unsoldered, Bias supply connected with jumper alligator cables, no output tubes, fuse didn’t blow. Conclusion, it looks that one of the cap in the doubler circuit is dead! BTW, festoons are also MIA… Same 163 VAC measured at red-red/yellow.

Thanks and regards,

Patrice
 
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163 is a bit low 198 is spec with 117VAC at the plug. Doubler cap is shorted in one of the sections. Replace all 4 can caps. Once you replace the can caps recheck all voltages against the schematic. 15% variance either way is generally acceptable. (168.3vac to 227.7vac). Both of my late model 400's show between 165 and 175 at the 1st 1/2 of the doubler. And they both run fine. Hayseed Hamfest has a 400 kit. https://hayseedhamfest.com/collections/fisher/products/fisher-400-re-cap-kit-4-cans You get options on the Bias Cap. 2 discrete caps or a Can cap. There's not as much room as most people think under a 400 for discrete caps on tie strips.

Electrolytics you have to replace are the FRAKO's. Rubber ended axials. 3-4 of them. Might have been good stuff when they were new but now about as useful as a Boar hog with Teats. Get rid of them. The ERO's are (or should be) fine. Pull a lead on each and check them if 5% difference replace.

Film caps to replace are the epoxy coats lack or brown "Dog turds". replace with your choice. C64 (.01 400v) replace with a X/Y cap .01uf of at least 300vac rating. This one is the "DEATH CAP" and as currently setup if it fails it will go shorted and you'll get zapped touching the chassis. X/Y "FAIL SAFE" or go open when they fail. I've gone to Murata for lead length as the kemets are set up for boards.
https://www.mouser.com/en/ProductDe...GAEpiMZZMsh%2B1woXyUXjxZuI/KWQWdPFGLEoi/3aV0=
 
Hello Larry, 163 VAC is with the PT HV secondary completely disconnected from the doubler circuit (it’s why the fuse was blowing). Should I worry about the health of this transformer?
 
According to member @bhamham , 163 should be ok! Obviously, my HV (red-red/yellow) is unloaded…

bhamham

Post in thread 'Fisher 400 Power Transformer'

Just took loaded AC measurements and with 119vAC house current, getting:
bias - brown to orange: 24.5vAC:
Fil 1: 6.3v green to ylw
Fil 2: 6.4v blue to white
HV: 155.2v red to red/ylw

Sorry, don't know your experience level but have DMM set to A/C and don't measure to ground. Measure each secondary pair, e.g. brown to orange for the bias
 
larryderouin said:
Above voltages are AC
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Thanks! So, my unloaded AC HV voltage is ok or not? bhamham mention 155 VAC loaded and you say it’s supposed to be more in the 198 VAC range in your first reply. It’s why I am confused…

EDIT: forget it, you said « above voltages are AC » (meaning 165 or 175 at the first half of the doubler). I thought the 198 mentioned before was AC.
 
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:lurk:

I have a 400 that has been on the shelf waiting for me to go thru for a long time. That and a X-202, lots of fun ahead.
 
Oh well... slowly but surely!

Power supply and bias supply recapped !

I used discrete caps and left cans in place. I won't post pics as it's not that pretty but it's safe and sturdy.

First DC node (405 v) is a bit high at 439 and all subsequent readings are also high but my AC wall voltage is 123-124 so it make sense.

No power tubes installed for now as I will, at bare minimum, install 10 ohms to ground first.

FM was tested sunday by connecting tape outs to another amp:

- FM mono is clean but the EM84 doesn't close as I am used on other sets. I think it's by design, right?

- On FM stereo or filter, EM84 closes more (again, by design?) but I am greeted with a strong "booooooooh" over the signal, not stereo at all!

I guess that the 19kc is received correctly as shown by the tuning eye but the 38kc is out of whack! C210 is not replaced yet so do you think that a bad 1uf could be responsible? Another cap in the MPX?

I hope it's the case because I am fearing someone tried to adjust the coils...

In any case, I have another Fisher MPX module with the three 12AX7's but intended to be used as an addon to consoles I guess. It wouldn't probably be a big deal to unsolder the original one and rig this one.

More to come...
 
That cap in the MPX unit going open makes for really weird stuff, so I'd throw a new one in and see if that doesn't sort it out.
 
By design, the eye tube does in fact close more in either of the stereo positions (although not necessarily fully closing), than it does on the mono setting — where the tube then functions as a signal strength indicator. The condition of the 1uF electrolytic composite coupling cap will not have any effect on the eye tube’s operation, but can make for garbled sound if bad. The MPX sub-chassis can be removed and repaired and/or aligned separately from the receiver as necessary if needed.

Dave
 
gadget73 said:
That cap in the MPX unit going open makes for really weird stuff, so I'd throw a new one in and see if that doesn't sort it out.
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dcgillespie said:
By design, the eye tube does in fact close more in either of the stereo positions (although not necessarily fully closing), than it does on the mono setting — where the tube then functions as a signal strength indicator. The condition of the 1uF electrolytic composite coupling cap will not have any effect on the eye tube’s operation, but can make for garbled sound if bad. The MPX sub-chassis can be removed and repaired and/or aligned separately from the receiver as necessary if needed.

Dave
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Will do it and report back. It’s really like a continuous tone over the signal, fingers crossed!

I know that you, @dcgillespie , had aligned MPX modules for some members here. I am in Canada however… Anyway, in case the 1uf isn’t the culprit, like I’ve said, the second module is almost identical to the onboard one, except one 1uf electro added (there are 2x1uf in the external).
 
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