Fisher 500-B Restoration Process for The New Guy

[Josey Wales]

Yeah, I picked up my Knight from the Goodwill site for a good price. It was originally a kit. It came with the assembly manual and a couple of books including some addendum tube tester settings. In going through it I found that almost all of the carbon composite resistors were way off spec. It's now fully restored and I can use it on my projects. It is a late enough model that I haven't bumped into anything I can't do gas, short and basic health tests with it. The ultimate test though is when you plug those tubes into your unit and they work great! BTW, the refurb of the tester was much easier than the refurb of my tube stereos.

Just be aware that there are parts for these tube testers that might be difficult to obtain such as meter movements, selector switches, etc. I was lucky with mine that all those parts were just fine.

Awesome and again, thanks for the information. I just spoke to a guy who has a B&K Dyna Quik Model 650 Tube Tester for $180 for sale here locally. I'm going to check it out this weekend. I'm not sure if it will even be able to test any of the tubes i have on the fisher but it's at least worth a try. He has a few others I will look at too but this one seems to be the closest to what i might need. Has anyone used this particular brand and model, I wonder?

 

[Josey Wales]

Yeah, I picked up my Knight from the Goodwill site for a good price. It was originally a kit. It came with the assembly manual and a couple of books including some addendum tube tester settings. In going through it I found that almost all of the carbon composite resistors were way off spec. It's now fully restored and I can use it on my projects. It is a late enough model that I haven't bumped into anything I can't do gas, short and basic health tests with it. The ultimate test though is when you plug those tubes into your unit and they work great! BTW, the refurb of the tester was much easier than the refurb of my tube stereos.

Just be aware that there are parts for these tube testers that might be difficult to obtain such as meter movements, selector switches, etc. I was lucky with mine that all those parts were just fine.

Awesome, thanks for the information. I just spoke to a guy who has a B&K Dyna Quik Model 650 Tube Tester available here locally. He wants $180 for it. Does that seem reasonable? I'm not sure if will even test what i need it to test but I'm going to check it out this weekend.

 

[1rebmem]

From what I read the Dyna Quik 650 was made starting in 1957 which predates the 7591 tube.
So it doesn't test 7591 tubes. You might be able to modify it to test them, there is some mention of this in google land.

The $180 price may be ok depending on the condition and what if anything has been done to it.
Being local and seeing it work is a huge plus. You won't have to pay for shipping also. Research the heck on the 650 before going to look at it.
Look into if it will test a 12AX7 also.

I bought a B&K 707 a few years ago and replaced all the electrolytic caps and then calibrated it. I'm not suggesting a 707 tester but I am suggesting if you buy one from the 50's or 60's you should plan on restoring and calibrating it. The later B&K's (707 and 747) do test 7591 tubes.
You could read about tube testers all day long to find out there is no perfect choice and the better rated ones cost much more.

 

[Tim D]

You might want to post about that B&K or read up to see if there are updated charts available that might cover your tubes. I paid a lot less than that for mine, but used prices are all over the place so maybe that price isn't outrageous - if it's already been updated.

 

[chip18sw]

Hello, Everyone,

I'm fairly new to the group and i've been using the valuable information on here for some minor projects in the past. Some great JBL 4311 posts about crossover updates etc. I want to say thanks for that. I have recently obtained a Fisher 500-B and I plan to restore it. My father had a Fisher set up in our living room for about 40 years so I'm certainly partial to the name. My father has since passed and In his honor I plan to get this amplifier back on the road to do something that I think he might have respected and in the process, learn as much as i can about this great amplifier. I'm ok with a soldering iron and I know the difference between caps, resistors and transformers but my knowledge on electrical stereo components is very limited. Schematics look like a foreign language to me. I want to do it right (without going for a degree in electrical engineering, too expensive, ha) so if I could get some advice or maybe some tips on the process it would be very helpful and I would be grateful. I'm sitting here looking at 4 tube amps I have purchased over the last 3 years thinking wow, is there anything better? Lol. After my research on here, I have noted some important steps to start with.

1) Replace the selenium rectifier? (where would I find one and what does it look like? What are the specs on it?)
2) Replace the caps? (Which ones? there are a lot of them)
3) I think all of the tubes are original and they don't look burned up like the others i've seen so i would just keep those
4) Are these kits on the auction site worth buying? A gentleman by the name of captain fantastic on there has a kit with an adjustable bias modification as well as the kit for replacing the insides of the cans on top.
5) The condition of the amp is pretty good cosmetically and all parts appear to be intact (all original) aside from some missing knob caps but that will be the finishing touch after cleaning etc.
6) I'd like this to look as original as possible
7) I was thinking of starting with something that might be easy to get a "win" and some confidence and then branch out form there.
8) Should i do this myself or pay someone to do it? I live in the Pittsburgh, PA area
9) Thank you for this awesome forum and all of the great information contained within it. I didn't know so many people loved vintage audio equipment like I do. I just thought I was weird. No longer. Lol.
10) Hopefully this thread made it's way into the Fisher forum as intended. Apologies ahead of time if it has not.
11) Pics of the amp to come shortly (I'll try to get a shot of the undercarriage)

WOW!! Well congrats and I'm pretty sure ... you already know but you are jumping into the "Deep End, of the Pool" with that puppy!

 

[Josey Wales]

WOW!! Well congrats and I'm pretty sure ... you already know but you are jumping into the "Deep End, of the Pool" with that puppy!

Lol. Yep. That's how I like to do things.

 

[Josey Wales]

From what I read the Dyna Quik 650 was made starting in 1957 which predates the 7591 tube.
So it doesn't test 7591 tubes. You might be able to modify it to test them, there is some mention of this in google land.

The $180 price may be ok depending on the condition and what if anything has been done to it.
Being local and seeing it work is a huge plus. You won't have to pay for shipping also. Research the heck on the 650 before going to look at it.
Look into if it will test a 12AX7 also.

I bought a B&K 707 a few years ago and replaced all the electrolytic caps and then calibrated it. I'm not suggesting a 707 tester but I am suggesting if you buy one from the 50's or 60's you should plan on restoring and calibrating it. The later B&K's (707 and 747) do test 7591 tubes.
You could read about tube testers all day long to find out there is no perfect choice and the better rated ones cost much more.

Thank you 1brebmem! I'm doing a lot of research on it now. More to come on that. I'm thinking I may end up taking the tubes to a local shop or I might hit up thornev on his offer to test them for me.

 

[Josey Wales]

You might want to post about that B&K or read up to see if there are updated charts available that might cover your tubes. I paid a lot less than that for mine, but used prices are all over the place so maybe that price isn't outrageous - if it's already been updated.

I'll ask him if it's been updated. he seems like a pretty knowledgeable guy so we'll see how it goes.

 

[Josey Wales]

Also, Could someone direct me to the link to the membership page? I feel like i've gotten so much great information from here already, i'd like to help support the group by submitting my donation. Thanks everyone!

 

[rufleruf]

Josey - looks like things are moving forward for you. I looked around, but I guess the "hey, become a member" stuff goes away when you're a member. On your user profile page there should be a link to subscribe.

I am about to build another IBAM for a 500B. You want me to build 2? You can have it for parts cost and shipping - seems like the efficiency of doing two would make it a quick project. I understand if you want the personal development project of doing it yourself.

 

[Josey Wales]

Josey - looks like things are moving forward for you. I looked around, but I guess the "hey, become a member" stuff goes away when you're a member. On your user profile page there should be a link to subscribe.

I am about to build another IBAM for a 500B. You want me to build 2? You can have it for parts cost and shipping - seems like the efficiency of doing two would make it a quick project. I understand if you want the personal development project of doing it yourself.

That would be absolutely awesome, Rufleruf! I was a little worried about trying it myself as I know i already have my hands full with the rest of the restoration. I'd be happy to send over the funds before you begin that way you're not digging into your own pocket for it. Thank you!

 

[Josey Wales]

That would be absolutely awesome, Rufleruf! I was a little worried about trying it myself as I know i already have my hands full with the rest of the restoration. I'd be happy to send over the funds before you begin that way you're not digging into your own pocket for it. Thank you!

Also, I just found the link to the member subscription page. Thanks again!

 

[tcdriver]

...I am about to build another IBAM for a 500B. ...

What does the IBAM stand for, in this context? When I did a web search all I got was Indian Board of Alternative Medicines.

 

[Josey Wales]

What does the IBAM stand for, in this context? When I did a web search all I got was Indian Board of Alternative Medicines.

Hello! I believe it stands for Individual Bias Adjustment Modification where you can individually bias each of the power tubes. I'm sure someone will be able to elaborate a bit more than I. I'm new here. There seems to be quite a few threads on the subject as I've been researching on here. I think if you do a search in here on "Individual Bias Adjustment Modification" you might have better luck getting some good information.

 

[Tim D]

Josey Wales called it correctly. Each tubes bias is adjusted manually via a potentiometer while measuring the current through the tube - usually with a multimeter. The difficulty with the IBAM I have on my Fisher KX-100 is that as soon as you adjust the bias on one tube it causes the current flow in the other tubes to move around. I have to go through the adjustment across all 4 output tubes a few times before they all have approximately equal current through them. Not a serious problem, but it is something to be aware of so that you don't just adjust each one and then think you are done. You have to go back to the first tube and recheck each one.

This is called a "modification" because these vintage amplifiers don't seem to have the components installed from the factory to do this - you have to add them as a "modification". There is another bias adjustment scheme with the same goals called an IBBA. I've been thinking that my next amp might use that instead (but I haven't made any final decisions.)

 

[tcdriver]

Hello! I believe it stands for Individual Bias Adjustment Modification where you can individually bias each of the power tubes. I'm sure someone will be able to elaborate a bit more than I. I'm new here. There seems to be quite a few threads on the subject as I've been researching on here. I think if you do a search in here on "Individual Bias Adjustment Modification" you might have better luck getting some good information.

Thank you. I have seen the IBAM so many times. I have even built an individual bias adjustment modification for my Fisher 500-C. I had just never seen the term defined.

 

[bhamham]

Josey Wales called it correctly. Each tubes bias is adjusted manually via a potentiometer while measuring the current through the tube - usually with a multimeter. The difficulty with the IBAM I have on my Fisher KX-100 is that as soon as you adjust the bias on one tube it causes the current flow in the other tubes to move around. I have to go through the adjustment across all 4 output tubes a few times before they all have approximately equal current through them. Not a serious problem, but it is something to be aware of so that you don't just adjust each one and then think you are done. You have to go back to the first tube and recheck each one.

This is called a "modification" because these vintage amplifiers don't seem to have the components installed from the factory to do this - you have to add them as a "modification". There is another bias adjustment scheme with the same goals called an IBBA. I've been thinking that my next amp might use that instead (but I haven't made any final decisions.)

It's a bit more straightforward on a fixed bias amp like the 500-B; that is each tube holds bias a bit better after adjustment. But I know what you're saying, it is tricky on those cathode bias amps like the KX-100 and it takes a few times at each tube before they're all the same.

 

[tcdriver]

It's a bit more straightforward on a fixed bias amp like the 500-B; that is each tube holds bias a bit better after adjustment. But I know what you're saying, it is tricky on those cathode bias amps like the KX-100 and it takes a few times at each tube before they're all the same.

My recent experience with my 500-C is a bit different. I have a fairly low hours set of 7591A tubes that I am using in my 500-C. When setting the bias two of them were fairly consistent, the two others showed variation VS time. How consistent the bias will be will depend a lot on the specific tubes. Tubes that do not hold bias well probably have some kind of defect that is not revealed when the tube is tested on a tube tester.

 

[bhamham]

Absolutely, it depends on the specific tubes and you're right most tube testers will not reveal bias weakness. Most testers apply around 150-180v and are not adequate for real operating conditions like 400v to the plate.

Are your 7591As new production like Tung-Sols or Electro-Harmonix?

 

[rufleruf]

Josey,

I have all the parts on hand to build you a board, so no worry about funds yet - I think shipping will be more than parts. I am going to Florida for Thanksgiving, so it will be after that that I finish it.

Here is the formula I used (Bruce deserves a lot of credit for making the instructions clear enough that I could figure it out without having to ask a bunch of questions) -same parts too: http://audiokarma.org/forums/index.php?threads/show-me-your-ibam-ibba-2016.713900/

And this is where I mounted it - just made one of the transformer studs long and mounted it between two nuts.


I can build you one of these, but it will cost you, and it's not very easy to deal with replacing the can cap.