610 Custom Electra III (440) Question

[audmod01]

For those who are familiar with the Fisher Custom Electra III, I notice that there are two push-pull amplifier circuits for stereo with the chassis pair. The radio tuner chassis has 6BQ5 output tubes and has a transformer with a 2.5 ohm output impedance. The companion separate amp for the other channel has 6BQ5 output tubes and a transformer with 4, 8 and 16 ohm taps. Why the odd 2.5 ohm output from the radio tuner chassis? I have seen 3.2 ohm speakers but not a 2.5 ohm speaker. Who made the 2.5 ohm speaker?

Joe

 

[larryderouin]

The CE III is the final iteration of the 510/560 or 610/560 combo as used in the '58 and '59 Consolette and companion units.The next year FISHER brought out the 440-A stereo amp in the C.E. IV.

The speakers are Jensen's from my recollection of my 610/510 consolette. In the consolette and companion you had 3-8ohm in parallel for about 2.5ohms or so. It was a squirrely set up but it works quite nicely. If you can find a 4-8-16ohm trannie from a junk 30xxx series 30A or a 8-16 ohm from a 20xxx series 30-A it should work, as the 510/610 amp section is predominately the same as the 30A. Use the pertinent NFB circuit to match the trannie. Then you can run 4-8-16 ohm speakers as you wish.

 

[audmod01]

Larry;
Thanks for the information. I had thought about several 8 ohm speakers in parallel to bring the impedance down. I had downloaded the service manual on the unit. I need to take a closer look at the details listed. The 6BQ5 outputs are capable of around 10-15 watts output depending on power supply etc. I noted the different feedback component values in the companion amp with the 4, 8, 16 ohm secondary transformer. Overall, a nice unit. Naturally there is no MPX circuitry since this was before the MPX method had been chosen by the FCC. There is a MPX output jack provided though, so MPX capability can be added without too much difficulty.

Do you have a picture of the control panels for the main tuner?

I am winding up my restoration of an E H Scott 800B, which has been a long process. Many caps and resistors to change plus lots of cleaning and polishing. I finally found a cabinet from a Metropolitan 16A to place the two chassis in. It is an amazing radio for 1946. It gets a Garrard RC-88/4 to replace a Webster Chicago 56-13 which came from a GE radio in the past. I am adding a 15 inch woofer with 5 inch coaxial mid-tweeter and crossover since the original speaker is long gone (from Parts Express). This will be my prize unit in the study. Soon I will get back to my Fishers!

Joe

 

[gadget73]

Nice 800B. I have one myself, but the chrome on mine is in pretty sad shape. I am fortunate enough to have an original Chippendale cabinet for the 800B though, but honestly that Metro cabinet is pretty darn similar. Same sort of bookmatch veneer patterns, etc. Mine had no changer, and it now has a Garrard Type A in there. I considered putting my RC88/4 in but mine is a mono changer and I like it for 78 duty. The 88 had a plinth, the A did not, so thats the one I went with.

 

[larryderouin]

The Custom Electra 610 Head unit got 3 more RCA's for MPX on the top panel just forward of the transformer as I recall. The Consolette in the previous 2 years didn't get them, so I installed them on my 610 in the consolette. I put a Sherwood A3mx MPX unit in the cabinet next to the head unit, spaced the 610 and the 560 about 6 ft apart and fired it up in FM Stereo. Slight separation adjustment with the SG-165 and getting 30-35db of separation. Very nice early stereo unit with MPX. Make the RCA Cables as short as possible (no longer than 3ft) and use low impedance cable.

I have the 440 owners manual in a scanned pdf. it's too large to upload here. If you need the O.M. PM me with your email address and I'll send you a copy email. Here's the page with the Front panel info.




I might have a pic of the front panel. Let me check my pics and I'll get back.

 

[audmod01]

Larry;
Thanks for the face plate image. That's good enough for my needs. The pix would be nice though when you get time.

I recently bought a Type A Garrard for my daughter to go in a different cabinet I am finishing up for her. The RC-88/4 is getting a Vaco/Varco type ceramic stereo cartridge with both 78 and LP needles so that any type record can be played with no damage. The E H Scott 800B had the Webster Chicago 56-13 changer complete with a GE VR cartridge, one of their first released. However it was not a Scott installed unit so I did not feel bad about changing to something else. Space in the Metropolitan cabinet is tight for an 800B, but I am managing to get it to fit (custom modifications while still retaining the slide-in front door under the tuner chassis).

Joe

 

[audmod01]

Larry;

I did a search through many Fisher files in the database and compiled a list of Fisher models that used 6BQ5/EL84/7189 push-pull output tubes. This is likely not all of the possible units but is a start if looking for donors of output transformers for the subject tubes with 4, 8 and 16 ohm secondary taps.

If you know of other models, please let me know and I will add them to the list.

Thanks in advance,

Joe

 

[larryderouin]

Looks good Joe. You can add the 20000 series 30A (look in the 560 companion Service manual) if you don't mind only having 8-16 ohms. T539-117 OUTPUT.

I'd tend to stick with the 20000 and 30000 series 30A as the primary and secondary voltages on the output and impedances are practically the same as on the 510./ 610 chassis. Which is what's in the CE III. I know it don't make a hill of beans but that's just me.

The 30A also came in a standalone and almost always was the 30000 series.

 

[audmod01]

Larry;
Thanks for the added units to include in the list.

I received the chassis from the eBay auction I won late today. This unit is rather heavy for a single output transformer plus power transformer, RF, IF, audio preamp stages and one output stage. I will watch for a viable option on the output transformer. 8 ohms is much more suitable for my purposes. If I decide to keep it for use in a system, I will need to find a escutcheon panel for it and knobs.

Joe

 

[audmod01]

I see that Transcendar has a replacement for the T720-116 that was used in the Fisher model 600 equipped with 7189 tubes, serial numbers below 50000. It is their part number TT-436-OT. Primary DC resistance is 300 ohms, primary impedance 7.7K ohms, secondary impedances 4, 8 and 16 ohms 20 watts, primary inductance 90H @ 120Hz, frequency response 10Hz-100kHz +/- 1dB @ 1W.

For their own transformers Transcendar mentions they use silver plated copper wire with teflon insulated wire leads. I am not sure if that is what they use on the Fisher replacements they offer I need to check. After looking at the transformer on the 610 chassis, I am not sure if the T720-116 type would fit physically. I probably need to contact Transcendar to see if I can get the physical dimensions and compare.

Joe

 

[larryderouin]

Transcendar hasn't been making transformers for about 6 months now. Whether they've gone out of business or not is anyone's guess. You might have to try Hammond or the other manufacturers.

 

[audmod01]

Larry;

I thought it odd that when I visited their website that there was no way to contact them or to order a transformer that I could see. Sad to see another manufacturer go out of business. As you say, look elsewhere. Thanks for confirming my suspicions.

Joe

 

[audmod01]

I wonder if any of our members might have an escutcheon panel and/or knobs for the Electra III. I would be interested in buying them if available.

Joe

 

[larryderouin]

Would measurements help???

 

[audmod01]

Larry;

Yes it would help! After I made that last post, I spent some time looking through the thread on the consoles and found several examples of the Electra III and it has a wooden trim panel plus the dial glass and knobs. The functional labels for the controls are apparently gold decals over the wood surface. The chassis I have has the dial glass but there is no wood trim panel with the control labels.

I have had a little experience making decals and might be able to make some for a trim panel to go with the unit. Alternatively I could use an aluminum plate and have it done by http://www.frontpanelexpress.com/ for a nice professional look - just some thoughts.

Joe

 

[audmod01]

Larry;

The Electra IV has an amplifier chassis 440 that uses a 9-contact female socket for interconnection with its companion tuner/preamp chassis. It looks like the socket has an offset larger contact of the size to accept the large pins used with say a type 80 rectifier or one of the older receiver tubes that had two large pins and smaller pins for keying. If the other 8 contacts of the socket would line up with the typical octal socket contacts, it might be possible to make a replacement plug using an octal tube base, removing the existing keying part of the base and then carefully drilling a hole at the correct position to line up with the large offset contact in the female chassis socket and install a large pin from a suitable donor tube base and re-flare the backside of the pin in the plug base while also using a small amount of 2-part epoxy to help secure the added pin. I don't know if anyone has done this, but it looks possible. I am eyeing a 440 amp on the internet that I could use with the Electra III chassis after defeating the 6BQ5 stage on the tuner chassis. The 440 amp has two output transformers with 8 ohm secondaries.

Joe

 

[larryderouin]

Joe; The 440 amp is self contained All of the pins on the 9 pin are power pins for the tuner/preamp anyway, and can be shunted internally and padded with resistors to compensate for the heater loads of the tuner and preamp for the 440. There should be 2 RCA Inputs on the 440 that you can use from the "A" channel preamp output, and come directly off the "B" channel output into the "B" channel on the 440.

I'd do it this way and leave the connector alone.

 

[larryderouin]

Give me a couple of days to get the 610 panel out and measurements made. It and the C.E. III panel should be identical.

 

[audmod01]

Joe; The 440 amp is self contained All of the pins on the 9 pin are power pins for the tuner/preamp anyway, and can be shunted internally and padded with resistors to compensate for the heater loads of the tuner and preamp for the 440. There should be 2 RCA Inputs on the 440 that you can use from the "A" channel preamp output, and come directly off the "B" channel output into the "B" channel on the 440.

I'd do it this way and leave the connector alone.

Yes, the 440 amp has its own power supply and as you said enough to operate the tuner it is often paired with. There is a 49T tuner on eBay I am watching. It has a Molex rectangular connector that would draw power from its companion 2-channel amp/pwr supply. It could be connected to the 9-contact socket of the 440 amp. I did buy the 440 amp today. I could still use the tuner from the Electra III and bypass the output stage on it and use both channels of the 440.

Joe

 

[audmod01]

Give me a couple of days to get the 610 panel out and measurements made. It and the C.E. III panel should be identical.

I thought that was the case after looking at photos of both units. Thanks in advance!

Joe