help me save a 400! My dad asked my to sell for parts but... ughg

realblues

Member
I am pretty new to servicing and diagnosing vintage components.

HELP ME SAVE THIS BEAUTIFUL 400!!! If you have an attention span and don't mind my long-windedness read below and PLEASE ADVISE

To be up front, I didn't compare apples to apples here so this isn't the best way to ask for qualitative advice but here goes: my dad asked me to pull a nice, clean 400 apart and part it out because: 1) it broke up at about 5 set flat - this was on a pair of 2-way bookshelf advents (8ohm) with 6" woofer(sorry no model #) and 2) output transformers are reading about 100ohms apart. Changing a transformer to try to match the "good" one at approx 98ohms is a possibility but my dad says that will only uncover more problems down the line.
I replaced most caps and resistors on this unit + Rectifier. It sounds close to a 500c until I get it loud with the Advents. Unfortunately I am stuck testing it on those advents..

Here's the kicker - I tried the same music on the 500c (fully rebuilt) in to Altec (again no model #) but they are huge - over 2' wide and almost 3' high (16ohm). They are 2-way with honeycomb grills... anyway sound was similar (trying to set aside the difference in tone of the speakers) but I can go almost full volume with no problems.

******* I think I am overdriving the Advents with the 400 but the numbers and the scope tell me a different story. All signs point to ONE funky output transformer. BUT, I am pretty new to this. My dad knows his stuff but I am doubting him on this.... but he has a much better understanding (he rebuilds and calibrates tube testers like the triplett 3444 & hickock 539c & Western Electric card-o-matic as well as it's hickock counterpart)

I WANT to save this unit from death and have a transformer on eBay I'm watching (if only I could get a matched pair??).

QUESTION: should I try to save this beautiful piece of equipment or scrap it out? Is the difference in my transformers OK (I can play for over an hour with no problems). With a transformer (assuming no other problems) my investment will exceed the value of a refurbished, trouble-free unit. This receiver will not be a keeper for me but I hate scrapping. I've seen my dad send so much awesome stuff to the recycler years ago because he didn't know the value or how it could be used - example hundreds and hundreds of transformers just tossed away...

If you read the entire post, thank you. And if you have advice to help me from sending one more unit to die I appreciate that even more!
 
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I'm just putting an idea out here. I'm not sure how appropriate these are for vintage Fischer gear but parts express sells a bunch of different types of transformers for tube gear.

Not sure if these would maintain that original vintage Fischer sound or not so I will let others chime in on that.

The good thing is at least you can get them in pairs if your are willing to fork over the $$$.

http://www.parts-express.com/term/t...m1010x497171x093741dc3bde4cebb39cee207a920c90

http://www.hammondmfg.com/1608.htm

No affiliation.

EDIT: Mouser also sells them.
 
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Luis; Part #'s between 400 and 500/800C are different. 7868 vs 7591 output tubes.
If the impedances are close I'd still have a bit of gas over swapping them tho.


To the OP. If your dad will let you keep it for your own, do it! There are plenty of 400 parts out there (make sure the part #'s match tho as the earlier transformers are somewhat different than the later ones and the feedback circuits are different.)

Look for the part # on the end bell's. Post the numbers on both. It's possible you have 2 different part #'s.

The Fisher is doing nothing except going UP in price. I'd keep it. Get some dummy loads and scope the hell outta everything in it comparing left and right sides. You might possibly be overdriving the advents. (Better speakers are a definate option here!) Read the "Improving the Fisher 400" thread. And all of the rebuild threads. Finish the basic rebuild 1st. (Are the can caps getting warm or hot during operation? If so replace them).

You could sell it as is, but you'd get below average resale because of the outputs. Absolute last option is to part it out.

I say FIX IT!
 
Some questions:
1. Did you check the foam on the Advent woofers? The surround could be disintegrating.
2. Does it distort on both channels or only one?
3. Did you try performing the adjustments in the service manual? Bias and center adjustments affect the point where the amp clips.
4. Did you try swapping the output tubes with the good channel?

This is just the easy stuff, there is more you can do before assuming a bad transformer, including wiring up the transformer from the good channel to the bad channel. Distortion can be caused by a bad coupling cap, bad tube, bad resistor. I will have a look at the schematic.
 
Have you tried listening with headphones? If you have a signal generator I would inject the signal into one of the inputs and look at the output and see if it has distortion, be sure to have a load on the output. I have not looked at the 400 schematic but the 500 and 800 have an pot in the phase inverter to minimize IMD. My vote is to fix it.
 
Luis; Part #'s between 400 and 500/800C are different. 7868 vs 7591 output tubes.
If the impedances are close I'd still have a bit of gas over swapping them tho.

Larry

I noticed my post was removed but no problem(apologies if I did a mistake to addres a ebay link!!!):drool:

FYI the 7868 and 7591 tubes are electrically similar also the 6GM5 is equal but with different socket and pin configuration, that's why I was recommending those trans with the advice if the s/n is less than 48001 because if is more than that the impedace in the OT change as Dave explains in the "improving the fisher 400 " thread.

Regards
 
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I'm with the fixit crowd! It's halfass working now so, believe it or not, you're more than half way there! AND you have the tools :thmbsp:

You've got that rumble in the channel and, like the Dr. said, it could be something as simple as a bad woofer, (try swapping the cables?) or a bad tube? Or cap? From what I understand from your post, it plays fine until you push it harder???? Just that suggests something other than the transformer......

If it were mine I'd a) fixit cuz you'll get your $ back down the line; b) pass it along as is so someone else can have a crack at it; Z) part it out and that is only after c through y which would include using it as a door stop, using it as a big paper weight, using it to flatten warped records, etc and etc. U'stand??
 
Some questions:
1. Did you check the foam on the Advent woofers? The surround could be disintegrating.
2. Does it distort on both channels or only one?
3. Did you try performing the adjustments in the service manual? Bias and center adjustments affect the point where the amp clips.
4. Did you try swapping the output tubes with the good channel?

This is just the easy stuff, there is more you can do before assuming a bad transformer, including wiring up the transformer from the good channel to the bad channel. Distortion can be caused by a bad coupling cap, bad tube, bad resistor. I will have a look at the schematic.

I replaced all caps that tested bad including good caps that were important, ie coupling caps. Changed a lot of resistors too. Can caps are OK & don't run warm. More answers:

1. The advents are in good shape. We use them as test speakers for whatever is on the bench at the time.
2. It distorts only on one channel. That channel's transformer has matching #'s but was clearly moved - I could tell by the pattern of grime I cleaned on the chassis.
3. Bias is my dad's department but I think what is when he noticed something funky...
4. And we did swap tubes and tried full matched set

While testing it out the first time the big green (yellow in some units) ceramic resistor that runs from the transformer to terminal 1& 7 on the outputs began to smoke.

The scope clearly showed one channel clipping bad using a fluke 199c.

Thanks everyone for the help and advice. I'm new to this but love it. The 400 is my dad's and if the repair price + purchase price is more than what he can sell it for he won't fix. If it was mine I'd fix it and hang on to it even though I have my own 500c. I just hate seeing these awesome units being torn apart. I'll see if I can find a good option otherwise its a goner... and such good shape too. I'll keep you posted if I win the battle!
 
Swap the phase inverter tubes. Also check to see if it is clipping going into the output tubes at the control grids. If it is check right out of the volume control to look at distortion.

Best of luck
 
Have you tried listening with headphones? If you have a signal generator I would inject the signal into one of the inputs and look at the output and see if it has distortion, be sure to have a load on the output. I have not looked at the 400 schematic but the 500 and 800 have an pot in the phase inverter to minimize IMD. My vote is to fix it.

Did that but without headphones - used a HP 200cd signal generator and used those huge gold Dale resistors to simulate a speaker load.

I'm lucky to have all sorts of cool test equipment my dad has accumulated over the years. Now if I only understood the circuits completely...

I think I can stall for a bit and try to source transformers while I work on this old Zenith 7G30 (6bq5 outs) that has been troubling me.
 
If it were mine I'd a) fixit cuz you'll get your $ back down the line; b) pass it along as is so someone else can have a crack at it; Z) part it out and that is only after c through y which would include using it as a door stop, using it as a big paper weight, using it to flatten warped records, etc and etc. U'stand??

Agreed. It would make the worlds coolest paperweight!
 
I replaced all caps that tested bad including good caps that were important, ie coupling caps. Changed a lot of resistors too. Can caps are OK & don't run warm. More answers:

1. The advents are in good shape. We use them as test speakers for whatever is on the bench at the time.
2. It distorts only on one channel. That channel's transformer has matching #'s but was clearly moved - I could tell by the pattern of grime I cleaned on the chassis.
3. Bias is my dad's department but I think what is when he noticed something funky...
4. And we did swap tubes and tried full matched set

While testing it out the first time the big green (yellow in some units) ceramic resistor that runs from the transformer to terminal 1& 7 on the outputs began to smoke.

The scope clearly showed one channel clipping bad using a fluke 199c.

Thanks everyone for the help and advice. I'm new to this but love it. The 400 is my dad's and if the repair price + purchase price is more than what he can sell it for he won't fix. If it was mine I'd fix it and hang on to it even though I have my own 500c. I just hate seeing these awesome units being torn apart. I'll see if I can find a good option otherwise its a goner... and such good shape too. I'll keep you posted if I win the battle!

That smoking resistor is a concern. With no signal, and a load connected, please measure the voltages on the output tubes pin 1, 2 and 9.
This receiver has no adjustment for the bias, and it can't be measured in the normal way because the cathodes of the output tubes are grounded. We can fix that but lets see if the voltages are at least in the ballpark.
 
I got a stay on execution. But have an open circuit between the red wire on output transformer and pin 9 (blue/yellow wire) on tube closest to power transformer. Pulling transformer for further investigation.
 
Plate circuit. That does sound like a bad transformer.

I was afraid of that!

I'm confident in my dad's diagnosis but I want it to be wrong and he is letting me explore and learn for myself. I'm doing all possible to save this receiver. I wish I knew a guy who was a mastermind at fixing/rewinding transformers... if that would help combining a newley fixed transformer and a used one. I'm still learning.

Crappy thing is my dad is moving and threw away 100+ transformers. He didn't know the value at the time but hey - live and learn. From my understanding transformers have to be made to work with the tubes and the needs of the circuitry so they seem pretty specialized.

As a side note, I picked up a heath kit AA-151 which is supposed to have great transformers. Its an AZ unit with not rust or corrosion and is in 9.5 of 10 condition. I just need to run it up on the variac and see if it works! Over the last year I've gotten tube fever bad!!

I have a 500c, '58 Bell 3dt with potted transformers and the AA-151 plus it's mono counterpart. And I'm just getting started buying up my own collection. Now if I could only get my dad's mc-60 mono blocks with pre-amps, his Eico HF-81, and ugh, his SS Marantz 2230 receiver... it does sound good for solid state.

Anyway, sorry for getting off topic.

If anyone knows a good source of info to understand transformers that would be cool. I know only their basic functions.
 
I was afraid of that!

I'm confident in my dad's diagnosis but I want it to be wrong and he is letting me explore and learn for myself. I'm doing all possible to save this receiver. I wish I knew a guy who was a mastermind at fixing/rewinding transformers....

I've read several many times guys here sing the praises of Heyboer Electronics. Easily found in Googie. Maybe someone will chime in on the appx cost to rewind vs. picking up a part at auction.
 
Heyboer is a very good choice. I used a number of their transformers in custom builds. Also Mercury Magnetics is also worth checking out. Both companies have a solid reputation.

Their is a wealth of knowledge on the net do a simple search on Understanding transformers and you will have a great place to start.
 
Heyboer will custom wind a 400 output. All you need to do is provide the old one. They'll even use the old endbells I've been told. But you need the spec's for it too.
Cost from $90 to $140 range.
Larry
 
Just interested, seems like you might have already learned a bit from your dad, but if I had a dad with the background that your dad has, I think I would like to spend more time with him, just saying!
 
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