Fisher 400 owners PLEASE READ....IMPORTANT!!!!

[dcgillespie]

Arts -- Very interesting! Almost as if the vendor manufacturing the transformers for your unit mis-marked them. At least the actual impedance specification remained the same as that for other later version units, in spite of the earlier version markings.........

And now ORP4's unit introduces yet another variation on the theme.......

Dave

 

[larryderouin]

Dave; Another option to the mix. (EDITED10-12-2015) Is it possible that, After FISHER used up all of the original transformers on the line, they went a year with just the "AX" transformers, as marked, then did away with the "AX" marking as it was the only transformers being used for the 400 and not needing to have the suffix any more. This is just a SWAG, So I think we're back to checking impedance.

With the dearth of 30000 and 40000 series so far, I would be inclined to leave the demarcation at the current point, and put a note in the manuals to check the impedance of the output transformers to verify proper use.

EDITED FOR CORRECT VALUES 10-12-2015
6400 ohms for EARLY (10001-47999) +/- 200 @ 47999.
10,200 ohms for LATE (48001 and up) +/- 200 @ 48001.

 

[dcgillespie]

Larry -- I'm confused with your comment on Fisher using up "all of the original "A" transformers". To my knowledge, up until all the last day or two, there were only two types of transformers: Those with the AX suffix, and those with NO suffix at all.

Arts unit threw a wrench in things by having NO suffix, yet being installed in a late version unit. It further complicates things by having the markings of a non AX transformer, but measuring like an AX transformer. Go figure on that one.........

The point is, that ORP4's unit is the ONLY one I know of that has transformers with simply an "A" suffix marking -- yet you are implying that there was a run made with "A" transformers. I know of no 400 service manual that calls out a transformer with an "A" suffix. Could you explain your comment further?

Early (no suffix) transformers -- that is, transformers with such markings that were actually installed on units with a serial number of < 48000 have primary windings that measure 6450 ohms. Transformers with the AX suffix that were installed on units with a serial number of > 48000 have primary windings that measure 10,200 ohms. And of course, Arts unit measures like a AX transformer as well.

It would be hard for me to imagine that Fisher would eventually drop the AX suffix on transformers for later production units, as that would make keeping track of replacement units from Fisher a nightmare!

Dave

 

[bhamham]

Dave, many thanks for taking the time to write up the instructions for measuring transformer impedance. Copied & pasted and filed with the many other tips you've given us.

 

[larryderouin]

Dave; Sorry about the confusion. Apparently somewhere down the road The Early version transformers became in my mind the "A" version, partly due to the original 32000 series 400 I had, had transformer's with "A" after the numbers, and the late being the "AX" version. And you're right, looking at the manuals there is no "A" suffix.

I agree, No SUFFIX for the EARLY models, and "AX" for the LATE model makes more sense from a standpoint of ease of identification. And it fits how the manuals are set up.

If you agree, I'll make edits to the initial request, making note of the NO SUFFIX for the early version, vs. "AX" for the late version.

I didn't think of the replacement parts thing on the Early vs. late versions.

Thanks for the constructive criticism. It helps keeping the different tracks that this could conceivably go off in, in check.

Larry

 

[arts]

What a can of worms!! When I dragged the 400 to the bench to check the impedance,my thought was ''well,there's probably no point to this; no AX code,gotta be the older lower impedance types,regardless of the unit serial number''.Imagine my surprise when I got the reverse; yeah,right!
After a lifetime in the manufacturing industry,nothing surprises or shocks me anymore.Between stock issues,poor communication between engineering,the floor,purchasing,suppliers and the ever present ''yeah,whatever'',even Boeing and NASA blow it out their a**es on a regular basis.

Dave,while your technique for transformer testing is an easily available and a simple but effective method,I'm not sure it's the safest choice for the inexperienced experimenter(maybe not even for the experienced old geezers either!) to be playing around with live line voltage.Shock hazard aside,there's much current on offer.
At minimum,I suggest adding to your instructions that a standard light bulb be inserted in one of the lines. At least that way,a fumbling of the clips will result in a bit more light as opposed to a face-full of molten metal

 

[dcgillespie]

Arts - I share your concern for safety around line voltage levels. Ideally, an isolation transformer should be used, and even an "appropriate" step down isolation transformer could be used -- all in the name of safety. The thought for using line level voltage, is that if you reduce the the primary voltage down to "safe" levels (via a step down transformer), then the secondary voltage can get so low as to introduce error from outside influence. Using the full rated line voltage will achieve the best accuracy.

For the purposes of this test however, only a general indicator is needed, so absolute accuracy is not required. Therefore, using a step down transformer would be the safest method. Even a Variac still can leave one side of the "drive" signal connected to the line, so simply using it to reduce the levels does not always create the safety it implies.

I have found that with appropriate (that is, well exercised) caution, the procedure is safe enough. There's less voltage with this procedure than when a newbie is requested to measure the plate voltage or other levels in an operating receiver. The bottom line is that safety cannot be over emphasized. But the very nature of this hobby has some risk relating to shock hazard. Those concerned about taking that risk should seek an experienced tech to measure their transformers.

Thanks for bringing up the concern!

Dave

Edit -- I have tried to go back and add a safety comment based on this discussion to the post I made regarding the procedures, but apparently the edit feature is time sensitive, as the edit button is no longer available to me on that post. I have edited my posts before under the new format -- but it was rather quickly after posting -- just as this one has been edited. However, there is no edit feature available any longer on the post where the procedures are presented. THAT's a change for sure!

 

[fred soop]

What a can of worms!! When I dragged the 400 to the bench to check the impedance,my thought was ''well,there's probably no point to this; no AX code,gotta be the older lower impedance types,regardless of the unit serial number''.Imagine my surprise when I got the reverse; yeah,right!
After a lifetime in the manufacturing industry,nothing surprises or shocks me anymore.Between stock issues,poor communication between engineering,the floor,purchasing,suppliers and the ever present ''yeah,whatever'',even Boeing and NASA blow it out their a**es on a regular basis.

Dave,while your technique for transformer testing is an easily available and a simple but effective method,I'm not sure it's the safest choice for the inexperienced experimenter(maybe not even for the experienced old geezers either!) to be playing around with live line voltage.Shock hazard aside,there's much current on offer.
At minimum,I suggest adding to your instructions that a standard light bulb be inserted in one of the lines. At least that way,a fumbling of the clips will result in a bit more light as opposed to a face-full of molten metal

Why not do the measurement reversed. That is, take a low voltage source such as a 6.3 volt transformer, connect it to the 16 ohm winding, then measure the primary voltage. That would eliminate all of the safety issues except connecting the meter to the primary wires.

 

[dcgillespie]

That's another good idea. There's lots of ways this can be accomplished. The bottom line is that one way or another, there is going to be relatively high voltage on the primary leads. Fred's way would certainly isolate the AC line which is plus, but not eliminate the shock hazard -- even inducing more voltage on the primary leads than the AC line would apply with the AX transformers. My approach was based on many AKers only have a DVM available to them. Ultimately however, each should use whatever approach they are most comfortable with relative to risk, in determining the turns ratio of their transformer.

Dave

 

[larryderouin]

Dave; The edit feature is only available when you are logge4d in. And to do anything except just reading you now have to log on everytime you access the forum. I haven't had any problems with editing even 2-3 days later.

Before the changeover, I would get automatically logged in (I'm running firefox), but now even if I check the stay logged on button, I still have to log on each time. Again this is probably one of the artifacts that have to be addressed by WARDSWEB. Or it may be that XENFORO doesn't allow automatic log on by FIREFOX, CHROME, etc. and they haven't turned on the "stay logged on" button.

 

[dcgillespie]

Thanks for the tip Larry -- except that it seems that our experiences are opposite. I've not had to re-log in each time (my name always appears indicating log-in status), but the little edit button is simply replaced by information dating when the post was made. I'll have to try re-logging in to see if that allows the edit feature to return on posts with some age on them.

Dave

 

[arts]

Well well,the plot thickens; These are the numbers (taken from photos sent by the owner) from a unit I serviced last month.Again,a pristine all-original unit,and no AX suffix;

SN: 77570 AM
OT: T1020-116-1
3946709
IF: 4 tube

 

[dcgillespie]

Arts -- That one would seem to mirror yours -- and particularly so if the transformers have the higher impedance primary winding. If so, I have no earthly reason why they would drop the AX suffix. In doing so, but retaining the impedance characteristics of the AX transformers, you would have had to specify not only the part number, but also the serial number for replacement. What were they thinking???

I have logged out and back in, and cannot edit even this morning's post. Man I hope that gets corrected!

Dave

 

[arts]

Dave, do you know at what serial # or year the 400 was discontinued? I'm thinking that 1967 was pretty late in the game for an all-tube receiver. If this was the end of the line for this model,quite possibly they were just clearing out whatever was on hand with no regard for future servicing issues. I'll try to measure his transformers in the future,If the opportunity presents itself.

Art

 

[dcgillespie]

Larry/Carter/Joe -- end production date for the 400 receiver? Must surely be in the late 60s at Art suggests.....

Dave

 

[larryderouin]

Sometime duriing 1968 model year Sept.68 to Aug. 69) After that Only the 1800 for another year @ Military exchanges overseas.

 

[arts]

I was expecting far more replies,judging by the number of times you see this model discussed on this and all the other websites.Not exactly a rare unit!!

 

[larryderouin]

Art; I think the difference is the technical level of the different forums. I see a lot of 400 threads on different forums, but they are more generic level questions (what caps, what tubes, etc.) where on AK we tend toward the whys' of certain circuits and improving the 400 while not changing the overall character of the unit. Most of the 400 rebuild threads here will end up being techinical discussions of the different improvements we've done on the 400 with the help and guidance of Dave, without which this forum would probably be another generic FISHER, where can I get this part, or what caps does everyone use (although we get our share of those too). This goes for all FISHER Units, not just the 400. The level of experience in general in this forum has gone UP leaps and bounds in the last 4 years. Most of that is, due to Dave G. He brings a unique and varied expertise to the forum and gives freely his time and experience to all.

Larry

 

[arts]

Larry-all good points. The technical level is definitely higher here than on most other forums,although diyaudio is also quite similar. As for Dave's input,what more can be said? And it's not just his tech-savvy; very few people have the ability to write in the technical realm with the level of clarity and precision that he can,yet still provide a thoroughly enjoyable read for both novices and experts alike. I'm very glad he takes the time to do so. In fact,I'm rather intrigued with his EFB concept. I have 3 units to try it with: Dyna SCA-35,Fisher 400 and a Fisher SA-100. When time permits(and we all know how that works!),I'll be doing my own before and after comparisons on each unit.
Hopefully, work will quiet down long enough to actually enjoy doing some bench testing of my own for a change. Now,if I can only get my old HP 3580A to stop going stupid on me occasionally......

Art

 

[bhamham]

I was expecting far more replies,judging by the number of times you see this model discussed on this and all the other websites.Not exactly a rare unit!!

My guess is that most have them hooked up and playing in a system, and it's difficult to get to the numbers. If they're in a case it's even more of a problem.