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Audio Transformer Diplomat D-39/Chassis T-290

J

Jim 2018

Active Member
So if one needs to replace the audio transformers, can one substitute any transformer that was designed for the ELL80/6HU8 tube? For example, if one looks there's some transformers from old Grundig equipment available (among perhaps other places if I look harder) that is designed for this tube.

Are there any other considerations or is it just a tube to transformer compatibility that is the issue?
 
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Jim -- I went to look at the schematic of your unit to see if I could help, and couldn't find on the Fisher Console website, but I may have overlooked it. I do remember the schematic however for the Philharmonic V, which also uses these output tubes as well, and likely in a similar if not identical design. It occurred to me however, that if you have:

1. A dvm, and

2. A variac, and

3. Can rig up a test power cord with some clips on the end of power cord, then we can measure your one good transformer to help find a replacement that can work.

It would also help if you know the impedance of the speakers this unit operates with.

Let us know!

Dave
 
The trick with subbing transformers is the feedback may need tweaking, especially if the secondary isn't the same. I have a 290-T here if you need some transformer measurements done. Output is marked as 8 ohm on the chassis.
 
Ah, so now we have that piece of the puzzle. What we need now is the the turns ratio of the transformer to determine the original primary impedance. If the transformer is physically small enough, I've often found that most replacement transformers of the same physical size will work acceptably as once below about a 15 watt level, the supersonic response characteristics are usually rather similar between transformers of similar impedance and power ratings, unless the original transformer is of very high quality (think Dynaco Z565, etc). I don't know what the power rating is of these amplifiers, but I guess that the primary impedance might come in at about 12K P-P.

Dave
 
FWIW I offered Jim a working ELL80 based console receiver (Philharmonic) I picked up on AK last year that works and would take care of his OPT and on / off switch needs.
 
dcgillespie said:
Jim -- I went to look at the schematic of your unit to see if I could help, and couldn't find on the Fisher Console website, but I may have overlooked it. I do remember the schematic however for the Philharmonic V, which also uses these output tubes as well, and likely in a similar if not identical design. It occurred to me however, that if you have:

1. A dvm, and

2. A variac, and

3. Can rig up a test power cord with some clips on the end of power cord, then we can measure your one good transformer to help find a replacement that can work.

It would also help if you know the impedance of the speakers this unit operates with.

Let us know!

Dave
Click to expand...

There are schematics out there...I found one for a D-38 and also a Philharmonic D-29 that use the same chassis and it is definitely 8 ohms. Unfortunately, the schematic does not show any specifications for the transformer. I could rig up a test if need be though I prefer not doing that just to avoid removing the transformer. Also I'm fuzzy on the wire output terminology (i.e exactly which is primary, secondary, etc.)

FYI...it sort of currently works. If I jiggle the Yellow/Blue striped input wire or apply pressure on the windings near where that wire exits the transformer, I can get it to work. It will from time to time produce popping noises and may go out (actually not out completely but rather to a very very low and very distorted sound).

For example, last night I ran it for a few hours and had it fail about an hour in. I unplugged the AC, firmly "squeezed" and "massaged" the transformer windings with my fingers, and plugged it back in. Ran the rest of the night no problem and little if any noise. Though this problem transformer is slightly softer than the other when it works thus requiring the balance shifted over to the bad side somewhat. Otherwise when it works, it sounds great! :)
 
rufleruf said:
The ELL80 is two EL95's in push pull in the same tube isn't it?
Click to expand...

I think my output tubes are good though I'd like to get another set and see they are expensive. I noticed that some people do this with two EL95s in each ELL80 socket. I may pursue this once I get everything else working.
 
gadget73 said:
The trick with subbing transformers is the feedback may need tweaking, especially if the secondary isn't the same. I have a 290-T here if you need some transformer measurements done. Output is marked as 8 ohm on the chassis.
Click to expand...

If someone can help me pin down an inexpensive substitute that would work properly based on measurements, I might take you up on that. Even though I removed the transformer once, I'm nervous about pulling it out again since it, for the moment, sort of works (I go more detail about that in my response to Dave).
 
rufleruf said:
FWIW I offered Jim a working ELL80 based console receiver (Philharmonic) I picked up on AK last year that works and would take care of his OPT and on / off switch needs.
Click to expand...

I appreciate the offer. I may take you up on that depending on whether I think what I have will be somewhat reliable as I test it more and whether I might find a less expensive substitute. Though this receiver you have, do you know for certain that both transformers are good and would work okay in my chassis? Even though the tubes are the same, I'm fuzzy whether that is the only thing that governs transformer compatibility/characteristics. And also, does the receiver you have use the same power/volume on a T-290 chassis?
 
The Fisher Philly transformer is basically the size of a Magnavox 6bq5 output. Its not big at all. Of course since the thing probably makes 10 watts, it doesn't need to be. Mine does sound good.

I "fixed" the power switch on mine using a similar switch I found on ebay. It doesn't mount the same though, and since the original was long gone I couldn't really try to adapt it. It had the same operator though. I ended up soldering it on the back of the control. Looks bad, works fine. I can't really get pics since the factory cap is also soldered in place, and honestly I don't want to tinker with it for fear of breaking something. Part I used was a Clarostat 5321, but that isn't the ideal one. It has one NC pair and one NO pair. What you want is a pair of NO (or is it a pair of NC??) so it will work like stock. Basically I have two terminals that are connected in the off position and two connected in the on position. What you want is two pairs, both connected in on, both disconnected in off. If you have the stock switch, I'd bet you could make the Clarostat add-on part mount into it, and just slip it onto the back of the control like the factory piece did.

I'll measure the transformers tonight after I get back from taking my mother to the doctor.

oh, primary is the side of the transformer connected to the output tubes. Secondary goes to the speaker.

If you're patient you can come up with ELL80's for a reasonable price. I have a spare lightly used Fisher set that I got for a price that didn't hurt too much. Whats in the thing is a strong set of ITT tubes that I think are Valvo or Lorenz, but could be Seimens. One of those German Phillips subsidiaries anyway. The Fisher tubes are also some German Phillips brand but not the same as the ITT ones.
 
oh, side mention, if someone is parting one of these out, I'd be interested in the discriminator transformer in the tuner section. Its the one marked ZZ50210-9 with possibly some extra letters after the -9
 
Please note, the understanding I have is that the primary winding of your defective transformer is intermittently going open. When/if it does go open, continued operation under that condition is very hard on the output tube the defective transformer operates with as the screen grid element in the tube affected must then absorb all the current flow, which it is not designed to do. As a result, the screen grid within the tube can be destroyed rather quickly when the tube is operated under that condition. It would be best to not operate the unit until a proper replacement transformer can be installed.

Dave
 
gadget73 said:
The Fisher Philly transformer is basically the size of a Magnavox 6bq5 output. Its not big at all. Of course since the thing probably makes 10 watts, it doesn't need to be. Mine does sound good.

I "fixed" the power switch on mine using a similar switch I found on ebay. It doesn't mount the same though, and since the original was long gone I couldn't really try to adapt it. It had the same operator though. I ended up soldering it on the back of the control. Looks bad, works fine. I can't really get pics since the factory cap is also soldered in place, and honestly I don't want to tinker with it for fear of breaking something. Part I used was a Clarostat 5321, but that isn't the ideal one. It has one NC pair and one NO pair. What you want is a pair of NO (or is it a pair of NC??) so it will work like stock. Basically I have two terminals that are connected in the off position and two connected in the on position. What you want is two pairs, both connected in on, both disconnected in off. If you have the stock switch, I'd bet you could make the Clarostat add-on part mount into it, and just slip it onto the back of the control like the factory piece did.

I'll measure the transformers tonight after I get back from taking my mother to the doctor.

oh, primary is the side of the transformer connected to the output tubes. Secondary goes to the speaker.

If you're patient you can come up with ELL80's for a reasonable price. I have a spare lightly used Fisher set that I got for a price that didn't hurt too much. Whats in the thing is a strong set of ITT tubes that I think are Valvo or Lorenz, but could be Seimens. One of those German Phillips subsidiaries anyway. The Fisher tubes are also some German Phillips brand but not the same as the ITT ones.
Click to expand...

Sounds like that Philly transformer would be too small...I think the Diplomat D-39 is 20 watts and I have some hazy recollection reading in some documentation it can momentarily peak at 36 watts.

As far as the switch, that reminds of a comment I wanted to make about it. It seems when the power is turned on or off, the original stock switch simultaneously does so for both the chassis and the turntable motor. From an engineering point of view (and I'm no engineer but have stayed in a Holiday Inn Express if you've ever seen that commercial :) ), I don't see why it's not just one pair switch that runs both. So if I could find a substitute switch that had just one pair, that would be fine unless someone could convince me why I might want to retain a two pair switch function.
 
A single ELL80 per channel probably only does about 10 watts at best. 20 watts might be power output total for both channels, 36 watts is probably one of the bogus "instant music power" or whatever measurements.

Anyway. From my Philharmonic 290-T chassis, transformer p/n T992-116-1, I come up with 9K, give or take a smidge depending which meter I wish to believe. They all agree within 2%.
 
gadget73 said:
A single ELL80 per channel probably only does about 10 watts at best. 20 watts might be power output total for both channels, 36 watts is probably one of the bogus "instant music power" or whatever measurements.

Anyway. From my Philharmonic 290-T chassis, transformer p/n T992-116-1, I come up with 9K, give or take a smidge depending which meter I wish to believe. They all agree within 2%.
Click to expand...

I am going to write Fisher and complain. That's a little levity. So when I read this I did a little Googling and I concede you are right about the 8.5 watts a tube. Then I started thinking, that's 17 watts if you add both channels. Fisher is advertising 20 watts. So I looked up what 12AX7 pre amp tube do and one source I found said it's 1.2 watts. I'm not sure it's accurate to add the pre-amp wattage. But if it is, then that's 19.4 watts. Nonetheless, what false advertising. So a T-290 chassis is basically a 8 1/2 watt per channel boom box?

Tonight I'm in the basement tinkering with the turntable. And I decided to Google the Garrad AT6 and watched a couple YouTube video. By sheer coincidence, the second one I watched was made by you in 2013. 'Tis a small world. Anyway, I didn't see you do any follow up videos. My turntable works but I can't get the automatic function to operate correctly. If I put a record on, then push the "record overarm" over, and then flip to the lever to automatic (which doesn't stay in automatic, I presume that's normal), the platter spins and nothing happens. If I fiddle and force the record onto the platter it plays beautifully. Any ideas?

Also, I appreciate the tranformer test results.
 
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