Fisher 800 vs 800B/800C

[EastPoint]

Hi folks. I picked up a Fisher 800 the other day. Really nice shape, partially restored. I can't find anything useful online about this one, since every search just brings up the 800B, 800C, and the occasional 800-T. What's the difference between this one and the later 800B and 800C?

 

[bhamham]

Try TA-800

 

[EastPoint]

Awesome, thank you.

 

[larryderouin]

The TA(Tuner/Amplifier. Later changed to Receiver)800 was the immediate predecessor to the 800B. The 800B was a 1 year product, However the 800c ran approx 6 years with incremental improvements, and a Multi voltage variant sold only to the Military as the 1800. The 800-T was the TOTL unit in 1969-1971 for FISHER. It was the Multi-voltage version of the 500-TX. The 800-T was/is Solid Stateas is the 500-TX. The Earlier models are all tube.

 

[fred soop]

The 800C was still listed in the Allied catalog as late as 1967 for $339.95.

 

[larryderouin]

That fits into the 5-6 year run.

 

[EastPoint]

So I powered it up on a variac and everything seems good. It’s had some work done. Cans don’t get hot and nothing is red-plating. Here are some pics. Does it all look ok?

 

[RS Steve]

I see a few original capacitors still in there, but most look to have been replaced. Add a CL-80 inrush limiter and screen stability resistors to insure the outputs stay healthy.

 

[EastPoint]

Sounds good. The CL-80 goes between one of the incoming AC lines and the power switch, right? How exactly do I wire the screen stability resistors? Are those 100 ohm 1/2w?

 

[dcgillespie]

Some quick observations:

1. The .002 uF coupling caps in the second stage of the line amplifiers are still original. These are not easy items to replace, but are of the type that leak significant DC voltage, and invariably do.

2. The cathode bypass cap in the first stage of the Channel B line amplifier is still original as well. Again, not a particularly easy item to replace. The cap may still be good. They don't classically leak, but they do often go intermittent.

3. Some of the cathode bypass caps look to be of the non-polarized electrolytic type, but I can't tell for certain. Such a cap will work in the application, but are not designed to have a constant polarizing DC voltage placed across them, which is the case in the application at hand. You might want to look closer to see if these caps are non-polarized types, or of the polarized type specified.

4. The power supply can caps may be running cool, but are showing signs of pressurizing from internal heat. It may be heat absorbed from nearby heat producing elements, or internal. But the sealing tar appears to be being pushed out somewhat now, which is a sure sign that pressure has been building. Whenever they are replaced, be sure to install Screen Stability resistors at that time as well if not already done.

I hope this helps!

Dave

 

[EastPoint]

Thanks Dave! I'll get cracking on those. Just to check, the CL-80 goes between one of the incoming AC lines and the power switch, right? How exactly do I wire the screen stability resistors? Are those 100 ohm 1/2w?

 

[dcgillespie]

Use 100Ω .25W pieces for the Screen Stability resistors. With that size, they will double as a fusing agent, yet allow the amplifiers to developed full sustained power output with narry so much as a yawn from them in that scenario.

The best way to install the resistors is to:

1. Cut the buss line connecting pins 4 and 8 of all the tube sockets together. On each socket, leave the jumper connecting pins 4 and 8, but cut out the part of the jumper running between each socket.

2. With the exception of the remaining jumper themselves, remove ALL other connections connected to either pins 4 or 8 at each output tube socket. When finished, all that should remain is the jumpers connecting pins 4 and 8 at each socket.

3. Daisy chain pin #1 terminals of each output tube socket together. When finished, all pin 1 terminals will be connected together.

4. Connect ALL of the leads removed in #2 above to terminal #1 on whichever tube socket is most convenient for the lead length of the component.

5. Install a Screen Stability resistor at each output socket between terminals 1 and 4.

The CL-80 can go on either side of the AC line. It is usually easiest to install it in place of the jumper connecting the one terminal of the fuse post, and one terminal of the Auxiliary AC outlets together. Leave the leads of the CL-80 full length, and keep it away from other wires and components -- it runs very hot.

Best --

Dave

 

[audmod01]

That fits into the 5-6 year run.

Larry;

I found a service manual from SN 51501 and up on Hi-Fi Engine. It shows the last 800-C series iteration, but does not show the power transformer used in the Fisher 1800 model. I recently acquired a late SN T991-116-1C output transformer that was from a Fisher 500-C and I am pretty certain that it was also used in the last 800-C and the 1800 units. It is just like the earlier versions with the exception that instead of having long bolts and nuts to hold the bells to the leaves and windings of the core together, it uses a long rivet and no nuts. The 1800 has a dual-primary power transformer so that it can operate on 120VAC or 240VAC. I assume that it may also have a switch on the back that allows user selection of appropriate AC input voltage (or a terminal strip in the chassis that allows the correct winding connections to be soldered into place). An adapter AC plug would be needed for operation on typical European electrical grids (or a different AC cord and plug). Some of our members who own 1800 models may be able to comment on the differences. Does a model 1800 service manual exist that is exclusive to that model?

Joe

 

[larryderouin]

No Exclusive manual for the 1800. The 51501 manual covers the 1800. (See front sheet at top.) Transformer strapping layout is on the TUBE LAYOUT page. The terminal strip that the transformer leads solder to should be long enough to accomodate the differences in wiring. Other than that the 1800 and 800c are same. Some later units came with riveted endbells/transformers due to manufacturer changes. The 800c and 500c used the same output transformers. The 500c and 800c (US ONLY) used the same primary transformers also.