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Fisher 400 help

Tubeglowpio

Tubeglowpio

Active Member
Hope some of you Fisher guys can help me with this Fisher 400 I payed good money for off of the bay, been wanting one for years so I'm hoping this one turns out nice. So since I have a chance to return this I have been doing some basic checks. So far I have only been able to get a few clean watts out before clipping. I noticed my high voltage on DC reads only around 300 volts and the AC reads about 100 volts. So I'm thinking what's going on is I have 100 volts of ripple and 300 volts DC? I get about the same voltages at the supply diode and the output tubes. I'm thinking the transformer should still be good and those voltage should be good once the power supply caps are changed. Thoughts?
 
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What voltages are you measuring, & where? Gotta get a lot more specific before anyone can help you. And what's a "supply"diode? Bias rectifier, perhaps? Bias supply is a negative voltage in relation to chassis ground. Post pics of the guts, we'll go from there. Everything you need to know about this model available on this site. Check fisher forum.
 
If the power transformer and output transformers are good, the power amp section can be brought back to stock performance, it’s just a matter of effort. First guess says if the amp is unmolested it just needs a standard restore applied to it. To do this restore yourself you’re really going to need a volt meter, an oscilloscope, and a signal generator.

I can’t tell from your description where you are measuring the high voltage line. Try measuring at the output transformer center tap connections. In the stock amp, that should measure something like 420V DC with maybe 2V to 3V AC ripple.

Also you’ll get better and more specific help on the Fisher sub forum.
 
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Sorry, posted right before bed last night guys. I have scopes, meters all of that as mentioned in my first message I'm pretty sure the power supply caps are really leaky as I can see the sine wave clipping after a few watts rms. Kward the output transformer voltage is reading only about 300 volts DC and when my meter is set to AC it reads 100 Volts so 300 plus 100 is close to that 400 volts I would expect correct? I'm hoping that once caps are changed most of all that ripple will be gone and my DC check should read around that 400 V. What AC voltage should I be seeing at the two red high voltage taps on the power transformer so the AC voltage before getting half wave rectified? I'm getting around 270-280 ish volts AC. If it checks out good there then I should be good to go. I know that when AC gets rectified the DC voltage is higher, its just that large AC ripple of 100 Volts I'm seeing that's kind of throwing me off. I've built and restored a few amps and luckily have not seen ripple this bad, plus most amps I work on I'm able to just pull the tubes including rectifier and check the tap voltages.
 
As far as output transformers I did check the resistance and both checked out the same and both taps from center tap measure exactly half of the total resistance so should be good there.
 
The high voltage secondary on the power transformer of the Fisher 400 is approximately 160V AC. That gets rectified through a voltage doubler (if working properly) to approximately 420V to 430V DC as I mentioned above.

It sounds like the first power supply filter caps are shot. I bet things improve substantially after recapping the power supply.

Good deal on your bench tools and experience. I couldn’t tell from just one post what you had or your experience level. ;)
 
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Sounds good, I think this Fisher will work out nice then, cosmetics are nice and has the wood case. All original tubes except the outputs which are Westinghouse, still need the tubes tested. It's the first model of the fisher 400, wonder how it compares sonically to the other 2 or 3 versions. I wonder if anyone has a parts list, when replacing the selenium bridge rectifier what value dropping resistor is used?

Yeah, I think a couple of the caps in the supply are shot, I think I'm going to get the cans replaced with that hayseed hamfest kit.

Thanks, still trying to learn something new everyday, still pretty young in the game of playing with electronics, about 7 years now. Just wrapping up my electronics engineering technician degree then on to the EE at ASU. Been working as an Aerospace RF tech for 6 months now so staying busy. Aiming to get to the level of knowledge that some of you guys have one day, there are a few technical gurus that really keep this site a great source. Thanks
 
I'm not seeing the Fisher experts and probably they haven't seen your thread yet. If you want more detailed and faster help you might ask an admin to move your thread to the Fisher area.
 
Check the Fisher forum, there's a lot of rebuild and troubleshooting info for the 400.

The Hayseed caps are good. I used them in my 400 rebuild over 10 years ago, they've worked well. When I was restoring my 400 a trusted AK member suggested that I increase the value of the power supply doubler caps. I did so, the receiver sounds nice.
 
Good ideas, I think I remember reading about the capacitor value increase, also heard if I change the coupling caps to go to .1uf Russian pio or mundorf silver/gold oil. I'm curious how the Fisher will sound compared to the Eico hf-81 I rebuilt, I'm hoping it's just as sweet but a little more 3D and better bass with the more power.
 
I have a Eico HF 81 waiting for restoration. Works now but can't comment on that part just yet.

To my ears, my 400 has a slight edge over my 500C. Its just a bit more smooth and refined.

I used Russian K40Y-9 caps for my 400. .1UF 630V. The suggested grid resistor change when using the .1 caps is around 220K. New production tubes have a hard time with the stock 330K resistors.
 
I really like the HF 81, only thing I still need is to replace the potentiometers, I ordered a treble pot from the captain on the bay and had the worst customer service of my life, would not recommend no matter what. Didn't receive what was ordered and the guy did not want to make it right and blamed me instead of reading the title he wrote, so never got the right pot, the pot I did get was not even as good as an alpha pot, bad tracking and felt a little cheaper. Looks like you have cornwalls, that's going to be my next pair of speakers maybe within the next year. Bet they sound nice with the 400.
 
Tubeglowpio said:
I really like the HF 81, only thing I still need is to replace the potentiometers, I ordered a treble pot from the captain on the bay and had the worst customer service of my life, would not recommend no matter what. Didn't receive what was ordered and the guy did not want to make it right and blamed me instead of reading the title he wrote, so never got the right pot, the pot I did get was not even as good as an alpha pot, bad tracking and felt a little cheaper. Looks like you have cornwalls, that's going to be my next pair of speakers maybe within the next year. Bet they sound nice with the 400.
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"the capatain" I know exactly who you are talking about. I ordered a volume pot for my Pas2. One section actually shorted for about 1/4 of the pots revolution. After a few days of being hassled he agreed to a return. Almost two weeks later I received a "replacement" pot. The replacement was the same defective unit I sent back! I contacted him several times and just got rude messages back. I had to open a claim and after a month I finally got my money back. Same time frame, I traded some parts and tubes with a friend for a Sherwood S8000III that I had. My buddy ordered a volume pot for the Sherwood and got the same junk. Replacement pot for the Sherwood is totally wrong. The loudness taper stays in circuit for about 3/8 rotation. Then, the Sherwood goes to nearly full volume. My buddy was so disgusted that he gave up and sold Sherwood back to me for almost nothing. I wish there was a way to let others know about this clown without violating any AK rules. If you find good quality pots for the Eico will you please let me know?? The pots are the biggest reason the HF 81 has been sitting in my shop for two years.

I love my Cornwalls. They sound amazing with tube gear. The only thing negative I can say about them is, they are very reviling Junk in, junk out. Bad recordings or an amp that isn't right are pretty harsh. The Cornwalls are heaven with a couple of watts from a nice single ended tube amp. .
 
dsndblm said:
"the capatain" I know exactly who you are talking about. I ordered a volume pot for my Pas2. One section actually shorted for about 1/4 of the pots revolution. After a few days of being hassled he agreed to a return. Almost two weeks later I received a "replacement" pot. The replacement was the same defective unit I sent back! I contacted him several times and just got rude messages back. I had to open a claim and after a month I finally got my money back. Same time frame, I traded some parts and tubes with a friend for a Sherwood S8000III that I had. My buddy ordered a volume pot for the Sherwood and got the same junk. Replacement pot for the Sherwood is totally wrong. The loudness taper stays in circuit for about 3/8 rotation. Then, the Sherwood goes to nearly full volume. My buddy was so disgusted that he gave up and sold Sherwood back to me for almost nothing. I wish there was a way to let others know about this clown without violating any AK rules. If you find good quality pots for the Eico will you please let me know?? The pots are the biggest reason the HF 81 has been sitting in my shop for two years.

I love my Cornwalls. They sound amazing with tube gear. The only thing negative I can say about them is, they are very reviling Junk in, junk out. Bad recordings or an amp that isn't right are pretty harsh. The Cornwalls are heaven with a couple of watts from a nice single ended tube amp. .
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Yeah, I found a manufacturer mentioned in another thread here who may be able to make some of the pots for the popular vintage amps that none of us can find a replacement for then buy some in bulk. I have a few single ended amps which was the original reason I started thinking about the Cornwalls. Currently the speakers I use the most are the Klipsch RP 600M, not bad for the price and work pretty well with anything 5 Watts or more.
 
Tubeglowpio,

Could you PM me the info too? I have a Fisher KX-200 amp in need of a new volume control w/switch. Thank you.
 
As to the original problem, invariably one of the voltage doubler caps has nearly failed open, producing the low B+ voltage. If the DC Heater/Bias supply is still (nearly) functional, then the output tubes will be biased nearly to or into a cutoff condition, the combination of which will produce little power output.

Dave
 
Alright guys I found the website, actually found it in another thread. Its oldradioparts.net, others have mentioned they had pots built so I wanted to check pricing for bulk of some of these pots we are all looking for.
 
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