diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Tubes / Valves (http://www.diyaudio.com/forums/tubes-valves/)
-   -   Fisher 600 questions (http://www.diyaudio.com/forums/tubes-valves/106105-fisher-600-questions.html)

akimball442 31st July 2007 01:51 AM

Fisher 600 questions
 
Well, I think (hope) I just got a once in a lifetime deal... Is anyone here familiar with the Fisher (TA) 600 model receiver?

I just picked one up. This is an interesting unit though. Built into a console (called the custom module) Is the receiver, and a drawer pulls out to reveal the barely used garrard turntable. Both of the original speakers are included also... along with all of the books that arent even yellow because they've been in an enevelope since 1959. This unit was sold as a complete set, called the model 90.

There isnt a mark on any of the woodwork and I got it for $100.

This unit is 100% original, and has all of the original Fisher branded tubes, most of which say made in Gt Britain, and appear to be mullards!


First the good: The tuner in this unit is amazing, on both FM and AM with only the built in antennas, and other radios in the house barely pick up anything. So I'm very pleased with that. Both of the magic eye tubes work, and work well. The dial lights up perfectly, and as I said, this is in new condition.

It has 7189 outputs, for a total of 20 watts per channel.

Now the bad: I'm not impressed with the sound of it at all. It's not really AWFUL... but both of my Eico's (the ST70 and ST40) far out perform it both tonally and power wise, and my little Magnavox 9302 will blow it out of the water as well.

This does not make sense to me, from what little I can find about it, it was very high quality (which is obvious just in the design) and people seem to love their Fishers.

The Bass is a bit much, even set flat with the loudness control off. The upper midrange is a bit overpowering as well, and the treble could be better.

Should I just dig in and start replacing all of the coupling caps.. or are these normal Fisher characteristics? I LOVE the look of this thing, and want to use it... I can live with the reduced power, but it needs to not clip so early, and the tone sure needs to impress me more.

I'll add that all of the controls work perfectly, are noise free-- this came from the original owner who had it in his dry, smoke free home.

Anyone with any ideas, or anyone who has one please reply! I'm interested in your opinions. Pictures to follow if anyone desires.

anatech 31st July 2007 02:19 AM

Hi akimball442,
Coupling caps!!!! Replace them !!
Filer caps !!! Replace them !!

If you don't do this, the unit may fail. Don't even run it.

I have a Fisher and it sounds nice. Don't expect this to run properly until you have fixed these problems. Also, Fisher liked to use Selenium rectifiers, you must replace these with silicon diodes and include some extra resistance to lower the rectified voltage.

What I've said applies to all old equipment, especially tube equipment. It's very sad to see a burned out transformer because someone felt they knew better. Even older Marantz solid state (and the others) need to be restored (this is by no means a repair).

I also own some nice Eico equipment, love them. Anything I run has been restored. Please don't kill your gear.

-Chris

valveitude 31st July 2007 02:25 AM

Based on the description of the sound, something is most definitely wrong. As an owner of an 800, I can tell you that this vintage of Fisher may not be the last word in accuracy, but what little errors there are of are of a euphoric nature..a very musical presentation.

When I first got my receiver it sounded like cat scat. A replacement of the coupling, as well as the bias supply caps, and the electrolytic cathode bias caps was the first step. I also replaced the selenium rectifier in the bias supply.

A few dollars in parts, and an afternoons work is all you need for an outstanding receiver.

Casey

Tom Bavis 31st July 2007 01:48 PM

If you don't have a schematic, it's in Sams Photofact folder 478-10. Not in my collection though...

akimball442 31st July 2007 03:56 PM

I do have a schematic, although it isnt EXACT. For example, it's definately the right model (TA-600), however, my unit has a line level center output.. which according to the owners manual is mono. I was curious as to which part of the amp this was derived from, I'm assuming it comes right after the preamp, because the owner's manual says that the volume and tone controls control it. The schematic does not have the center channel.
All of the tubes and other components are the same from what I can tell, so I think it'll be useful for repairing this amp. I'll check when I get home (I am at work right now) as to which number is on the schematic. Thanks for posting the SAMS number.. The schematic I have is a copy of the SAMS' schematic, so I'll see if they match up, or whether the one posted in this thread is a different one.

I had figured that this unit would need some work, given it's age, but I'm wondering whether or not it's safe to leave the tuner sections alone, as they function perfectly. I'll replace all of the power caps, and coupling caps, and check the condition of the resistors.

Someone mentioned a selenium rectifier... I'm wondering if this has one.. as I said, I do not have the schematic handy, but I know it has two tube rectifiers. One is a GZ34, the other is a smaller one, I forget which. EZ90 maybe..

Thanks for your posts, I'll keep this thread updated.

Aaron

anatech 31st July 2007 06:10 PM

Hi Aaron,
You may find selenium rectifiers in the bias supply and the heater supply. I haven't got this schematic, but my 400 C preamp uses a DC heater supply (25 VDC, series strings of two heaters in three sections for 6 tubes).

Your Fisher should sound very good.

-Chris

Eli Duttman 1st August 2007 12:25 AM

Aaron,

Googling for a schematic turned this up, which contains some interesting info.

The 2 rectifiers are a 5AR4/GZ34 and a 6V4/EZ81. Both are used to generate positive rails.

The O/P tubes are self biased. The phono section heaters are in the O/P tubes' bias circuitry. There is no negative supply in the unit.

An external MPX adapter is required for FM stereo. If you don't have the adapter, Steve Bench "rides to the rescue" here.

------------------------------------------------------------------------------------

The 20 WPC rating says the O/P tubes are 7189As, which are rare and EXTREMELY expensive. IMO, while you are recapping, you should make the changes needed to use 7189s as the O/P tubes. The Russian 6p14p-ev/EL84M is a true 7189 equivalent that's affordable. 17.5 WPC is not at all shabby, when long term serviceability is taken into account.

When O/P dissipation is reduced to a level suitable for 7189s, you can no longer place 12AX7 heaters in the bias circuitry. An external regulated 12 VDC supply will have to be built.

anatech 1st August 2007 01:01 AM

Hi Eli,
Thank you. It looks like my 400-C and FM-100 combo. Knobs and all!

-Chris

akimball442 1st August 2007 02:05 AM

The one I have is slightly different, for example, the antenna connections are not mounted horizontally with the screw connections on top as shown in the photo. Mine are oriented like the speaker connections, and line jacks, horizontally on the back of the unit.

Also, mine seems to have just plain 7189 tubes... not 7189A. I wonder if this could be a problem?

The schematic I have does not specify "A" tubes either, just 7189... same applies to the label on the back of the cabinet.

Furthermore, there is NO solid state recification of any kind in this unit. I have gone over the schematic from left to right using a ruler... and all rectification in this amp is done with tubes.

The phono preamp does get it's heater supply in the fashion you mentioned though, interesting. A good idea too.. I need to do that to my blessed Eico ST70- DC heaters. The phono stage in that thing is pretty nice, but so noisy..


I'll be the first person to take a screwdriver to the bottom of this unit since it left the factory in 1959... COOL! I don't think I own any piece of equipment that someone else has not repaired or butchered over the course of time. This thing is truly 100% original, and I cannot wait to hear how it sounds when I finish.

Aaron

anatech 1st August 2007 02:11 AM

Hi Aaron,
Quote:

Also, mine seems to have just plain 7189 tubes... not 7189A. I wonder if this could be a problem?
No. There may not be any real differences that apply to your amp. What you will buy these days as a replacement would be a 7189A. I have a couple amps that need those type of tubes.

Quote:

Furthermore, there is NO solid state recification of any kind in this unit.
Cool. Relax then.

Quote:

A good idea too.. I need to do that to my blessed Eico ST70- DC heaters.
No you don't. There is nothing wrong with AC heaters. I prefer them. If you want to really improve things, bias them up 30 ~ 50 VDC from ground. Lose the hum balance pots (that are grounded). You can leave them in the chassis.

Quote:

The phono stage in that thing is pretty nice, but so noisy..
Phono stage where? My Fisher 400-C has the phono stage tubes mounted on rubber grommets. :cool:

-Chris


All times are GMT. The time now is 11:22 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio


Content Relevant URLs by vBSEO 3.3.2