Pilot 240 Output transformers

[Ziradog]

I took this amp in trade a while back, and I did so knowing that one of the output transformers had been replaced with a Stancor (unknown specs). I have been browsing for a correct transformer while I work on other projects, run an ad on Bartertown & ongoing searches on other sites, but no love. I have found other Pilot EL84 push-pull amps & receivers but they use different number transformers. The SAMS for the 240 does not list a replacement transformer (other than the Pilot one), but does list the specs.

I have not done anything to the amps as it sits, not power with variac or DBT. I was hoping to locate a transformer before starting.

So, do I just continue to be patient? If I decide to use another transformer or presumably pair of transformers (like ones from the EL84 version of the 903 for instance), what issues do I look for? Or other suggestions (I have enough boat anchors already so don't go there)?

Thanks.

 

[gadget73]

If you can't get an original, a pair of good ones from something else would be the next best option IMO. You may need to tweak the amp to make sure its properly stable but its certainly not impossible to make it work well. Frankly I'd go for the best transformers you can fit and afford. Not sure what the original footprint is there, but if the Dyna ST-35 iron is a fit I'd be awful tempted to go that route.

 

[Ziradog]

Gadget, the tweaking would probably be beyond my abilities, that's why I was thinking something close to the originals. The current OPT's are not especially large.

6DZ7, I will open it up & look. I know it says Stancor on the top, where is the number usually located?

BTW, the SAMS info for the Pilot OPT says Primary 7400 ohms, Secondary 16 Ohm tap @ 8 Ohms (?)

 

[shelly_d]

Edcore might be able to help. They currently have these 3 transformers in their lineup. They have also, in the past, been known to wind one of these series to specialized impedances for a reasonable fee. You might want to contact them and see if they can help.

https://www.edcorusa.com/xpp15-7_6k

https://www.edcorusa.com/gxpp15-8k

https://www.edcorusa.com/cxpp10-8k

Good Luck

Shelly_D

 

[Ziradog]

Interesting. Is 8K input impedance "close enough" to 7.8K? The first one (and the cheapest) doesn't go real low on the frequency response (70 Hz). The last one is only rated for 10 watts - EL84 push-pull should be over that I think?

So if I did this (or something similar), how do I know what adjustments the feedback loop will require, especially since these have 1 or 2 taps, and I probably would not pick 16 ohms for my tap?

 

[FlaCharlie]

I've never gone this route but I've heard of others sending units to Heyboer to either be rewound or duplicated. I assume you don't have the dead original so you'd have to send them your good one and have them clone it. There's actually a chance that they made the original since they provided transformers for numerous manufacturers back then. I've heard nothing but praise for their work.

https://www.heyboertransformers.com

Otherwise you'd just have to find some off the shelf model with similar specs that would physically fit.

 

[Ziradog]

 

[primosounds]

It is too bad about the bad the OPT. Well, the replacement Stancor trans might be better than anything you can get nowadays. Once the cover is on only you will now the difference

 

[shelly_d]

Interesting. Is 8K input impedance "close enough" to 7.8K? The first one (and the cheapest) doesn't go real low on the frequency response (70 Hz). The last one is only rated for 10 watts - EL84 push-pull should be over that I think?

So if I did this (or something similar), how do I know what adjustments the feedback loop will require, especially since these have 1 or 2 taps, and I probably would not pick 16 ohms for my tap?

Your amp won't put out much more then 12 to15 watts top of it's EL84 outputs. Worst that would happen would be the early onset of distortion due to core saturation. You won't be running it high enough to do damage to the tranny. I assume you have some space issues to deal with as well.

As I said in my first post, they have done custom winds in the past. My recollection is seeing posts on here about a $20 or $40 fee to do the custom wind. Very reasonable in my opinion.

Choose a form factor based on what space you have and contact them with your power and impedance needs, primary and secondary. See what they tell you. You have nothing to loose at this point.

 

[multichamp12]

If you really want to get an OT made, or buy one, I would actually measure the turns ratio and impedance of the original OT before ordering anything. I would not trust the sams manuals to always be accurate.

As I suggested in your thread on BT, it will probably be a good idea to just buy another 240 as a parts unit and take the OT from that, I have seen multiple 240 amps sell for around 200 in the past number of months.

 

[Ziradog]

Good point on the turns.

On the other, as I mentioned there, I hate to gut one usable unit to fix another, and 200 is on the high end of what the unit is worth at this point (i.e., tubes, recapping, etc. to be done). I would probably buy another to restore & part out this one if it came to that. But at least some of the options here are less costly (the Edcore transformers listed above are ~$50 each for instance).

 

[primosounds]

Good point on the turns.

On the other, as I mentioned there, I hate to gut one usable unit to fix another, and 200 is on the high end of what the unit is worth at this point (i.e., tubes, recapping, etc. to be done). I would probably buy another to restore & part out this one if it came to that. But at least some of the options here are less costly (the Edcore transformers listed above are ~$50 each for instance).

Dog, you should check what the replacement transformer that is specified for this unit. Back then the exact replacement transformer was specified and there were usually several brands recommended. The Stancor unit might be an exact replacement in terms of specifications.

 

[Selmerdave]

It might be easier to find another Stancor, can if you can find the model number, and depending on that it might be a very good one.

 

[Ziradog]

I might be able to find that in a catalog if you have the number on it?

Finally got time to open this up. Looks like the number is A-2855. It does not have end bells, and is roughly the same size as at original OPT. Any info you can find on it would be great.

I also fired the amp up with my DBT. It does play and only a little hum. Pots are very noisy, and one channel is noticeably weaker than the other (hopefully due to a dirty volume or balance pot), but it does play ok. If I ever get my current project (Grommes 40PG) done, I think the pilot will be good.

 

[Ziradog]

Not surprised, but I am disappointed.