Possible replacement for Fisher 400 Output Transformers

[TravAndAlex]

I recently picked up an early version 400 in pretty rough shape with the plan to refurbish it. As project funds are limited, it was a very unhappy surprise to learn that both output transformers are dead (no continuity on primary windings - I've tested pretty thoroughly and although it is rare to have both die, I'm reasonably confident this is the case with this one).

I've contacted all the transformer repair, rewind, replace options that have been suggested (Fisherdoc, Transcendar (not currently active), Gary Brown, Brian Sowter, and Heyboer) and the least expensive to date has been replacement transformers for $120USD each plus shipping to Canada from Heyboer. This is beyond current budgets and may make the refurb unobtainable.

This is until someone suggested checking with EDCOR. They can build exact duplicates for approx $85.00 each plus a one time design and setup charge of $350.00. Or they offer an off the shelf model for $54.60 the CXPP25-6.6K transformer.

THAT PRICE MAKES THE OFF THE SHELF OPTION VERY ATTRACTIVE!

Now this transformer does differ from the original. Most obviously with a single 8-Ohm secondary (not 4, 8 and 16) which if it would work, is fine with me as I would use the 8-ohm speaker connection anyway. It is 6.6K Ohm Primary Impedance rather than (going from Trancendar's spec sheet) 6.4K. FULL SPECS AND DIAGRAMS ARE AT THE BOTTOM OF THIS POST.

The question I have for you experts is: could the EDCOR transformers work? And by work, I mean sound good in this application? I absolutely understand this is no longer going to be 'stock' as originally intended. However, at this price I can go ahead with getting this unit working again, vs perhaps just having to sell or part it out.

What would have to be done to make them work? I assume I could just ignore the 4 and 16 Ohm taps and just hook up the 8 Ohm as normal?

The original just has 2 plate wires and a B+ on the primary. The EDCOR has these 3, plus 2 screen wires. What would be done with the additional 2 screen wires?

Would anything else need to change on the Fisher to make this work? I've picked up Metalbone's refurb kit (of course before I tested the output transformers - yes, very stupid I know).

TRANCENDAR
Early Fisher 400
Fisher Part Number T 1020-116
For Receivers with Serial Numbers Lower than 48000
6.4K Push-Pull to 4, 8, & 16 ohms 25 Watts
Frequency Response: 10 Hz to 100 kHz +/- 1 dB @ 1 Watt
Primary DC Resistance: 225 ohms
Primary Inductance: 90 H @ 120 Hz
Part Number TT-429-OT
Weighs 3.8 lbs. (1.7 kg)


EDCOR CXPP25-6
Wattage 25W
Primary (input) Impedance 6.6K Ohms
Screen/Grid Tap 40%
Secondary (output) Impedance Depends on model.
Frequency Response 20~20K Hz., <1dBu
THD+Noise <0.1% @ 1K Hz.
Bobbin Material Nylon 6/6 GF-30
Flamability Rating Class B 130°C
Core Material M-6 29 ga. grain oriented lamination steel
Secondary Insulation (transformer) Clear air dry polyester varnish
Termination UL1015, 20 ga. lead wire
Mounting Powder coated steel end bells
Color RAL 5010 Gentian Blue
Weight 4.5 lbs.
Compliance RoHS & REACH



I greatly appreciate any advice and guidance you can provide!

 

[Dadbar]

My experience with Edcor is that while they make very nice stuff, they build to order so you will be waiting weeks to get your delivery (you should ask them what the current lead time is).

In that same period of time, a set of Fisher 400 trannies are likely to come up on Ebay if you are patient, and in the long run, the original ones will make you much happier. If you are getting the Edcors as a stop gap until you find the real thing...and you have a future use for the Edcor, then it might be worth doing it.

By the way, are you sure that both trannies are really dead? The reason I ask this is that I've had weird issues in the past trying to measure Fisher trannies (in my case, for a 500C) using a DVM. The inductance of these trannies put my Fluke meter into a weird oscillation that initially confused me and I thought they were toast. I now only use my classic Simpson 260 analog meter for verifying trannies.

 

[knockbill]

Hmmm,,, with the two orders I placed to Edcor, both arrived in a week to 10 days,,, I hear of their long lead times, but haven't experienced it... The screen wires can be coiled up and taped off,,, if you find an original pair of OPTs you can reuse the Edcors in a new build, or such...

 

[TravAndAlex]

Here is the insides of the better of the two. If you look closely you can see three breaks in the wire due to (green) corrosion. I'm assuming there is no way to fix this when no wire sticks out from the winds.

 

[gadget73]

if you can't get anything to connect to, you're pretty much stuffed on that one unfortunately. Once in a while you get lucky and find that it breaks but there is enough to connect to again. Looks like this one suffered from moisture.

One thing to be aware of when changing output transformers is you may need to fiddle with the negative feedback circuitry some. Not looking at a schematic, but its pretty common for the NFB to tap from a 16 ohm or whatever the highest impedance output tap is. If your replacement transformer doesn't have that, at a minimum you'll have to adjust the resistor value to maintain the right level of feedback. There is also sometimes a small cap across the resistor, and that might need to be tweaked to get it to behave optimally.

Edcor does make transformers with multiple impedance outputs, just no idea if they make a 6.6K with those. The 8k ones I have on my Magnavox amp have 4, 8 and 16 ohm.

 

[TravAndAlex]

One thing to be aware of when changing output transformers is you may need to fiddle with the negative feedback circuitry some. Not looking at a schematic, but its pretty common for the NFB to tap from a 16 ohm or whatever the highest impedance output tap is. If your replacement transformer doesn't have that, at a minimum you'll have to adjust the resistor value to maintain the right level of feedback. There is also sometimes a small cap across the resistor, and that might need to be tweaked to get it to behave optimally.

Here's the advice I've been given on that:

The loop global NFB comes from the 16 Ohm tap on the original. With an 8 Ohm substitute, divide the feedback resistor by 1.4 and multiply the feedback capacitor by 1.4 to get the same amount of NFB. If you're really fussy you test the stability of a square wave through the section and tweak to feedback cap value to get well damped ringing. But most people don't bother as long as the HF response isn't rolled off or peaky.

That sound right to you?

 

[TravAndAlex]

Hold the phone. With a bit more searching... turns out that there is an Edcor 30W 6.6K with the 3 secondaries! Is there any problem substituting a 30W transformer in the place of the original 25W? Does anything need to be changed in the original circuit to do so?

Wattage 30W
Primary (input) Impedance 6.6K Ohms
Screen/Grid Tap 40%
Secondary (output) Impedance 4-8-16.
Frequency Response 20~20K Hz., <1dBu
THD+Noise <0.1% @ 1K Hz.
Bobbin Material Nylon 6/6 GF-30
Flamability Rating Class B 130°C
Core Material M-6 29 ga. grain oriented lamination steel
Secondary Insulation (transformer) Clear air dry polyester varnish
Termination UL1015, 20 ga. lead wire
Mounting Powder coated steel end bells
Color RAL 5010 Gentian Blue
Weight 6 lbs.
Compliance RoHS & REACH

 

[fred soop]

The photo in post #4 looks like there may be enough wire to connect new leads. You have nothing to lose by working on it. You may also be able to very gently pull on the good wire to expose a bit more for the connections. If you can make it work, then you can split the outer insulation in the middle, peel it back in both directions, and anchor the new leads.

 

[dcgillespie]

The problem with using replacement transformers that are anything other than the original device is their sub and supersonic characteristics, which the published specifications of general replacement transformers indicate nothing of. It is these qualities that give some indication as to how well the transformer will operate within an existing NFB design. Invariably, the use of generic replacement transformers will require adjustment of the NFB compensation and HF stability components, and even then, still may not provide the same level of performance as that of the original transformer. If you cannot repair the original or locate original replacement transformers, I would consider the use of general replacement transformers as a last ditch option.

Dave

 

[arts]

If you think the transformers are pricey,wait till you see the shipping

 

[TravAndAlex]

If you think the transformers are pricey,wait till you see the shipping

Yup. Cost of 1 of the transformers again to ship the 2 of them to Canada.

 

[arts]

Yup. Cost of 1 of the transformers again to ship the 2 of them to Canada.

This seems to be a common problem with any US orders. I guess they're trying to pass on the ''FREE US SHIPPING!!'' costs to their Canadian customers
I was looking at some high-precision collet's for my router; $30USD to ship a twenty buck part.
RobotShop tried to rook me $50USD for a $115USD order the size of a box of Kleenex.
Both examples (and several more) refused to use a less expensive shipping method .Are they kidding!?!?

This,apparently, is a common trick used by retailers. That,and ''handling'' fees.In my case,not gonna happen.

I was very interested in a few Antek power transformers I need for repair work,as they meet my requirements perfectly,have a great reputation, and are very inexpensive compared to other brands. After considering the exchange, shipping,customs and duty costs,I'll be sourcing some shitty Canadian-made Hammond's locally.

 

[bhamham]

Yea, I don't get why it's so expensive to ship from the states to Canada. I recently tried to ship a Fisher receiver with wood case (50 lbs) to Montreal and it was $180 for USPS and $210 FedEx, that's nuts. Less than $50 to ship to Ohio with FedEx where it eventually went. No way to treat our good neighbors.

 

[whoaru99]

Yea, I don't get why it's so expensive to ship from the states to Canada. I recently tried to ship a Fisher receiver with wood case (50 lbs) to Montreal and it was $180 for USPS and $210 FedEx, that's nuts. Less than $50 to ship to Ohio with FedEx where it eventually went. No way to treat our good neighbors.

Have you every done customs paperwork?

I don't know how it applies to this situation but I've had occasion to try doing it for work-related items. IMO it's worth every penny to pay an expert to do it.

 

[bhamham]

I lived in the UK for seven years and sent loads of heavy boxes and parcels to the US/Canada, Asia, Australia, NZ. Yes, completing an easy to fill customs form. No where near as expensive as it is to ship things from the US overseas. I paid an expert to send my car to the US, but for items like audio gear it strikes me as overly expensive. Just my opinion.

 

[whoaru99]

I lived in the UK for seven years and sent loads of heavy boxes and parcels to the US/Canada, Asia, Australia, NZ. Yes, completing an easy to fill customs form. No where near as expensive as it is to ship things from the US overseas. I paid an expert to send my car to the US, but for items like audio gear it strikes me as overly expensive. Just my opinion.

Where do you suppose the high cost comes from? US companies just socking it to their customers, or maybe the non-US countries have higher import tariffs or whatever that go back into the export shipping cost?

I know, for example, when we ship a machine to Brazil the price basically doubles because they tax the crap out of it. Of course, that's new equipment of a different nature but maybe it's something similar? Dunno...

 

[bhamham]

Good question. I've found that stuff ship from Canada to TX seems reasonable when I browse ebay or CA online vendors. Maybe its profit taking from shippers b/c they can, don't know. I've found since back in the states that cell phone service is much higher here than in the UK, and internet/cable TV service too. Of course, gasoline is cheaper than bottled water here.

Back on topic, we need to find some output transformers from a 400 for TravAndAlex and get them shipped as cheaply as possible to Canada.

 

[N8Nagel]

My experience with Edcor is that while they make very nice stuff, they build to order so you will be waiting weeks to get your delivery (you should ask them what the current lead time is).

In that same period of time, a set of Fisher 400 trannies are likely to come up on Ebay if you are patient, and in the long run, the original ones will make you much happier. If you are getting the Edcors as a stop gap until you find the real thing...and you have a future use for the Edcor, then it might be worth doing it.

By the way, are you sure that both trannies are really dead? The reason I ask this is that I've had weird issues in the past trying to measure Fisher trannies (in my case, for a 500C) using a DVM. The inductance of these trannies put my Fluke meter into a weird oscillation that initially confused me and I thought they were toast. I now only use my classic Simpson 260 analog meter for verifying trannies.

Hmm, sidebar - I wonder if that was throwing me off when I was measuring the OPTs on my Scott 340B

Got unbelievably strange readings on resistance with both my Flukes, but got good reasonable readings when putting them in continuity buzzer mode.

I hadn't dragged out my Simpson meter at the time as it was broken but I've since obtained two 260-8Ps "for parts" that both actually work with only minor problems, so I'm taking a break from gear fixing to fix those up. I should recheck with Simpson before resoldering the leads...