Mating a Fisher 440 Amp to a 490-T Tuner

[audmod01]

Larry;

Thanks for that note on the magnetic cartridge situation. I was uncertain what to expect there. I did not think Fisher would expect the Electra VI to use a ceramic cartridge. I thought about the possibility that I might have connected some of the B+ to a lower than needed voltage source going to the preamp stage, however I don't think I did. I can do a quick check to verify the plate voltages of these tubes just to be sure.

I did some listening yesterday to several stations on FM and the sound is quite good overall. It is not as good on the low end as my AR-2Ax speakers, but then the original cost of the XP-55B compared to the AR speakers is an indication of their performance. With cabinet installed speakers there is always the issue of mechanical feedback to a turntable or changer. Really deep bass notes can cause a stylus to jump the groove and so Fisher, like others, had to incorporate some restriction on low end response to avoid that. I did use greater value coupling capacitors throughout to help with this issue. Overall, I am pleased with the results.

If the physical balance of the cabinet with all equipment installed turns out to be an issue, I might add some more ordinary metal handles on the back of the unit as additional stabilizers for carrying. That way two hands could be used in carrying the cabinet.

Joe

 

[audmod01]

Larry;
I found an Audio-Technica SC35C cartridge which is designed for DJ use and features up to 5G tracking force and a 5.0mV output level, 20Hz-17kHz response and is stated to have resistance to skipping groove. This might be a good choice for a teen-ager who is not used to dealing with cartridges, needles and records. I am sure there are others that will work too, but this one popped up in a search I did.
Joe

 

[audmod01]

Here is a revised speaker wiring diagram that reflects the latest determination using an ohm meter. The connections depend on the wire colors at the speaker switch. The schematic refers to S1 Front and S1 Rear, but in the unit I have S1 has neither front nor rear sections. Instead there is a single wafer switch with what might be described as top and bottom switch sections. It is actually a double-pole triple throw switch.

I should add that one of the two 12AX7 preamp tubes turned out to be really noisy. I had to replace it. This also helped the volume of the weak channel. It sounds much better now.

Joe

 

[larryderouin]

Sounds like a plan. I have a spare Pickering/Stanton 500.V3 (updated versioin of the 500AL)with a fairly new stylus on it(<100hours), if you want, for shipping. Are you using a Garrard or the Miracord. I DO have a spare headshell from a 10F that should fit the 40 IIRC. If a Garrard which one. I might have some Type"A" headshells. This way she can cartridge roll without worrying about the lineup of the cartridge on the headshell. The Pickering/Stanton is good from 2 to 5gr.

Spec's
Stanton 500.V3 Tech Specifications

• 
  Spherical Stylus
• Stylus Type: Spherical .7 mil
• Special High Polish
• Frequency Response: 20 to 17 kHz
• Nominal Output @ 1kHz: 4.6mV
• Channel Separation @ 1 kHz: 28dB
• Channel Balance @ 1 kHz: within 2dB
• Tracking Force: 2 to 5 grams
• DC Resistance: 535 ohms nom.
• Inductance: 400 mH
• Cartridge Weight: 5.5 g
• Tracking Ability: 80µ @ 3 grams
• Recommended Load: 47k ohms and 275 pF
• Replacement Stylus: N 500

http://www.stantondj.com/stanton-cartridges/500v3.html

 

[audmod01]

Larry;

The Stanton 500.V3 has specifications very close to the Audio-Technica DJ unit I found. I will get with you off-list.

this afternoon I cut a 1/4" plywood piece for a back cover on the cabinet. I have the cut-out for the Aux Inputs to the 490-T done along with the antenna terminal strip, and a cut-out along the bottom for the speaker terminal strip. Still to be done are openings for ventilation and the AC cord.

Do you think I should stain this back cover or leave it natural? Most cabinets I have seen leave the back cover natural, although E H Scott receivers tended to have the back covers of their cabinets stained although not sanded and varnished.

Joe

 

[gadget73]

A Shure SC-35C would also be an appropriate sub for the Pickering or Stanton. They're still in production, sound good, and are not stupidly priced.

 

[larryderouin]

So would the Shure M44.

 

[audmod01]

Gadget and Larry;

I saw both a few minutes ago and they are viable options too.
Here is a picture of the Elac Miracord 40A tone arm and cartridge mount piece from the manual:

Joe

 

[gadget73]

I run a Shure SC-35C on my Garrard Type A. Needed a cartridge, had that one laying around with no stylus so I bought one. I'm impressed, it sounds very good and its a fine match for that machine. No experience with the M44 but its also an old Shure body like the SC35 is. Kinda funny that they are now "DJ" cartridges, at one point they were hifi record changer cartridges. The Stanton stuff is the same, the same styluses meant for record changer duty became the hot ticket in the DJ world. My other favorite changer cartridge is a Stanton 680e.v3 which were selling brand new for about 40 bucks a few years ago when they were on clearance. I bought several.

 

[audmod01]

One strange thing I discovered about this Miracord changer is that there is no way to secure the spindles. They just drop in and when I use the automatic spindle I have to remove the spindle before removing records that have finished playing. There is no retainer clip. The support tabs of the spindle do not retract when the record is pulled up the shaft and the whole spindle begins to lift out of the turntable. I thought it was a lack of lubrication and have lubricated the automatic spindle, but it still does it. Using one's fingers it is not possible to make them retract while the spindle is in the changer or removed. This spindle was not originally with the changer. I bought it from eBay and maybe it has a problem internally. I am not sure as this is the first Miracord changer I have dealt with in many years.

I am going to reinstall the OEM cartridge that came with the changer and check operation again. It may have higher output than the Audio Empire 888pe that I put in yesterday - TBD.

Joe

 

[larryderouin]

That's one of the foibles of using a Miracord. You have to remove the changer spindle to remove the records. I'm not fond of it but it(the spindle) works better than either the Garrards and Duals with that type. When it cycles there is a locking arm that actually pulls down on the spindle and holds it during cycling and then releases it. With the short spindle, you can reverse it so you can either run it and play the record as a single or repeat continuously until you turn it off. It's a weird system but it works very well.

 

[gadget73]

Many Garrard changers work the same way. Some you can fight the records off without pulling it, but there is not a reason to. The Lab 80 uses a spindle very much like the Miracord, you pull it to flip the stack. Or you pick the stack up and the spindle comes along for the ride.

 

[audmod01]

I guess I should have taken the time to read the entire manual on the Miracord. Thanks Guys for the information! At least now I know it is operating like it is supposed to. I have been a fan of Garrard changers most of my life, so I know their peculiarities pretty well.

I have the back cover inside in the study for some additional work to finish it. The slot for the power cord remains to be done and that will not take too long to do. Then the remaining efforts will be securing it to the back of the cabinet and applying labels for the antenna connections and the speaker terminals.

I had a voice mail from the battery company which was to create a battery for the RK-20 remote hand unit. They have finished that effort and I just need to go by and get it and pay the fee. There is also the Philco 46-1226 radio-phonograph that needs the BSR model 310 changer adapted to the unit for my son-in-law. I may be able to finish that before Christmas too. That will be good so that I can then devote more time to working on the MF-300 and the RK-20 restoration.

Joe

 

[larryderouin]

I vote that JOE be Inducted into SANTA's ELVES ASSOCIATION, (FISHER DIVISION). (I didn't get much sleep last night).

 

[audmod01]

I recently noticed that the bass response of the phono inputs of the 490-T tuner/preamp chassis was rather thin compared to that of the radio circuits. I decided to increase the values of the coupling capacitors in order to improve the response. C9 and C10 were increased from .01uF to .047uF and C12 and C13 were increased from .022uF to .1uF. In the process of making the changes I discovered that the physical layout used by Fisher where the Channel A and Channel B inputs are located between 12AX7 V8 and 12AX7 V9 resulted in them making a change that does not agree with the pin-outs shown on the schematic for V8. The input of V8 from the RCA phono jack for Channel A goes to pin 7, so the cathode for that half of the tube is pin 8 and the plate is pin 6. Going to the second half of the tube, the coupling capacitor C9 places its output to the grid at pin 2 where the cathode for that half is pin 3 and the plate is pin 1. The reason they did this is just simple convenience of layout, construction and shorter leads and contributes to greater immunity from hum pickup as a result. The moral of this is, don't be surprised if you see this in other products where a double triode is used which has equal characteristics for each half of the tube. It makes no difference which half of a 12AX7 is used as the low level input and which half is used as the output.

The changes I made here improved the bass response of the phono circuits to equality with that of the radio circuits. This is OK to do for a case like this one where the speakers are not part of the same cabinet as the phonograph source. In a console with speakers in the same cabinet mechanical feedback can become so severe that bass notes can cause the stylus of a changer or turntable to bounce out of the groove of a record while it is playing. Even in cases of separate cabinet for a changer or turntable mechanical feedback can become an issue to deal with. Experimentation as to physical placement of speakers and changer/turntable may become necessary to eliminate bass feedback problems.

Joe

 

[audmod01]

The stereo was delivered and our granddaughter is currently enjoying listening to some Christmas LPs, starting with John
Denver's album and others will follow. She is thrilled. It is complete with a custom owner's manual for the stereo and the Miracord changer instructions are included.

Now to work on one for the other granddaughter! I have a start on it with the Fisher 500-C.

Joe

 

[gadget73]

Probably some LF filtering for the console environment. Sensible, when you put the turntable in the speaker box you're just asking for feedback if some care isn't taken.

I'm sure she's very delighted to have such a nice piece of gear that has so much effort into it.

 

[audmod01]

Gadget;

Yes, Fisher deliberately restricted the low end response for that very reason - low frequency audio feedback. It can make listening to disc records almost impossible in worst cases. Dave Gillespie has commented about this issue too. At least it is easy to correct for by changing capacitor values.

Merry Christmas and Happy New Year to all of the group!

Joe

 

[larryderouin]

Joe;
Did the cartridge arrive? It should have been there y'day.

Larry

 

[audmod01]

Larry;

Yes the cartridge did arrive in good shape on Tuesday. I have a BSR 310 changer I bought to install in the Philco 46-1226 which has a Shure M75CS in it. That one has a tracking force range of 3 - 5 grams and an output of 9.3mV which puts it pretty high for a magnetic cartridge. It is supposed to originally have had a blue stylus grip color but now has a beige color which is was indicated to work from 1.5 - 3 grams not sure of that though since it may be a replacement. In any case the one you sent will go into the Fisher. I can then remove the Empire 888pe and put the Shure unit in it.

Thanks a million for going to so much trouble!

Joe