Finally IBAMed the heck out of my 500-B

[RS Steve]

I finally felt comfortable digging into my very early 500-B and installing a individual bias adjustment board. Took a little expert advice from Larry to get me there, but now it's done. There was no place on top or out back on this chassis to mount the board, so I did away with the test points on the board and mounted under side.

Not only is this receiver eye candy, but the sound is over the top too. Pretty odd to see the 7591's in front of the OPT's and in their own oven so to speak (early versions had them this way). All the more reason to make sure they run cooler. After a total recap, new diodes, new rectifier, screen stability resistors, sampling resistors, LED lamps, and a so so batch of two different pairs of power tubes, all is good. Before installing the IBAM, the tubes were running in the .50V range so it made it impossible to use confidently. Now I have them doing around .34V and I'm quite pleased with the results. This is one of cleanest receivers I have, and quite the time capsule sporting all original small tubes.

.

 

[AlTinkster92]

Very Nice Steve!

 

[Dave451]

Nice work, Steve. Sounds great and looks great, too!

 

[larryderouin]

Compared to the "C" models and the 400 how much ventilation (holes for vertical convection) is surrounding those tubes? I'd remove the baffle to dissipate some of that tube heat. It can't be good for them. Otherwise I like it. Glad you got it all sorted out Steve. Larry

 

[audmod01]

I agree with Larry. The original had the shield behind the output transformers, but no shield between the output tubes and the driver/phase inverter tubes. If you then put the unit in a typical Fisher cabinet, you could get an AC low noise fan to place behind the unit and provide some extra ventilation to keep things cool. You could also add EFB which would drop plate dissipation on the output tubes if you have not already done so.

Joe

 

[RS Steve]

Compared to the "C" models and the 400 how much ventilation (holes for vertical convection) is surrounding those tubes? I'd remove the baffle to dissipate some of that tube heat. It can't be good for them. Otherwise I like it. Glad you got it all sorted out Steve. Larry

I checked them after playing for a good hour with my heat gun, all 4 were right at 268 degrees. I have seen higher temps on some of my other units.

 

[RS Steve]

I agree with Larry. The original had the shield behind the output transformers, but no shield between the output tubes and the driver/phase inverter tubes. If you then put the unit in a typical Fisher cabinet, you could get an AC low noise fan to place behind the unit and provide some extra ventilation to keep things cool. You could also add EFB which would drop plate dissipation on the output tubes if you have not already done so.

Joe

EFB school is now in session, it will take this electronics dummy some time to graduate though.

 

[Catmanboo]

By all means leave the shield between tubes & transformers. Being black, they will most assuredly absorb mucho heat if it's removed. If you could polish the tube side, that'll help reflect more heat from the transformers. And yes, a little fan can't hurt. I run one whenever using my x101d & 500c's. Imho, no such thing as too much ventage on these things.

 

[larryderouin]

Cat; The shield in the front which wraps around the side is the one Joe and I are talking about. 268 isn't bad for 7591's as mine on the X-101-B run at 280 each (and it's running Cathode bias). But the X-101-B has open air all around the tubes. This is encased almost like the output's on as Sansui 1000A. And those get up in the mid 300's if the POWER REsistors aren't replaced/moved.

 

[ZR9B]

Very nice!!! Is the face silver? Looks great.

 

[RS Steve]

Very nice!!! Is the face silver? Looks great.

It has the more gold face on it, maybe this picture shows it better.

 

[ZR9B]

Yup... like mine.

 

[RS Steve]

Compared to the "C" models and the 400 how much ventilation (holes for vertical convection) is surrounding those tubes? I'd remove the baffle to dissipate some of that tube heat. It can't be good for them. Otherwise I like it. Glad you got it all sorted out Steve. Larry

Here you go Larry, looks to have plenty of vent holes around the tubes. I'm thinking that it has a pretty good flow upwards, and from my testing, temps seem pretty stable at 260 - 270 degrees. I'm thinking they added the inner shield for having it in a wood cabinet, it would limit the heat migrating forward and direct it out the screen opening in the top of the cabinet. I doubt the shield is needed when using the unit with no cabinet.

 

[RS Steve]

Thought I'd post the transformer numbers here also, OPT's are T-860-116-2 and the PT is T-860115-5
Maybe Larry can chime in on what dates these are.

 

[larryderouin]

The pertinent #'s are under the FISHER #'s Steve. (2nd line)

 

[RS Steve]

Okay, how about 926132

 

[Rockyhill]

What do those numbers indicate? Date code?
On my 500B (s/n 35591N or M):

OPT (can only see one)
T860-116-3A
9268287

PT
T-860-142A
9263286

 

[larryderouin]

Steve 32nd week of 1961. 926 is manufacturers code for.....TODD ELECTRIC CO. Yonkers, N.Y.

Rocky; Both made by TODD. PT shakes out to 28th week of 1963. OUTPUT doesn't make sense unless the 1st 8 is actually a 3 then it would be 28th week of 1963 also. you can both get the 1961, 1962, and 1994 EIA booklets from Tom Bavis site...... http://www.audiophool.com/Techno.html

 

[RS Steve]

Steve 32nd week of 1961. 926 is manufacturers code for.....TODD ELECTRIC CO. Yonkers, N.Y.

Rocky; Both made by TODD. PT shakes out to 28th week of 1963. OUTPUT doesn't make sense unless the 1st 8 is actually a 3 then it would be 28th week of 1963 also. you can both get the 1961, 1962, and 1994 EIA booklets from Tom Bavis site...... http://www.audiophool.com/Techno.html

Wow, 1961 500b, 57 years old and still in such clean condition. Thanks Larry!

 

[larryderouin]

Mid to Late August build on the transformer then add 3-4 months for logistical train to kick in from manufacturer to Fisher, production, then shipping to distributor, and finally store. This is a 1962 model due to that. Probably sold sometime between Halloween and Christmas at earliest, and worst case it sat on the shelves for 2-3 years and got sold as a 65-66 model.

Frannie has the original sales slip for my Executive. It sat in the store up until 1966 when it was finally sold. Italian Provincial wasn't really popular (personally I think it looks 1000% better than French provincial. my personal feelings on this aside, FISHER probably sold 10-20 Modern Cabinets for every F.P or I.P. cabinets sold). Note to self. Get that Sales Slip from Frannie.