ERIC Mod 3460P Restore

[parvo3]

I just bought this Amplifier on ebay recently and it worked for
a short 30 minutes until the primary coil burned out on the output
transformer on the right channel. I purchased a sam's photofact for this amplifier and for the short time I had it running on my Altec mod 14's, it sounded superb. This impression that I had with this amp may be somewhat biased by the fact that I am so
spoiled with using solid state products since the late 60's. This
is a far cry from a Mac or a Mark levinson but I hope to find it worthwhile to restore this amp back to it's new and operational state.
I have the transformer removed and I have examined the burn spot to confirm that the device is indeed burned. It has 3 leads
coming in for primary and 3 for the secondary. I would like to upload some photos of the unit and the photofact to give you a better illustration of this unit.
I have been trying to shop around for a replacement transformer
but the specs and appearance seems to be a lot different and I am afraid replacing the transformers with the wrong specs and doing more harm than good.
From the photofact: each output transformer has the following data: primary:6100 ohm tap @ 30%
From the schematic: 310v primary (blue) (from plate?)
320v pri tap? (brown) (from grid?)
333v pri ? (red)

16 ohm secondary green
8 ohm tap Yellow
com black

The preamp stage has 1 12AX7A
The AF stage has 1 ea 12AX7A (each channel)
Outputs are 1 ea EL84 (each channel)
I suppose the rectifier is EZ81 or 6CA4
a total of 6 tubes
I am trying to establish some sense of what is on the amplifier so taht I may be able to ascertain the approximate output of this amp. This will be instrumental in finding a suitable replacement output transformer.
So My question is in 3 parts.
1) could you be able to guestimate for me the output rating of this amplifier based on the info that I have posted so far?
if so, what is it?
2) What would you recommend in replacing the transformer? 2 new ones or a near match on the old?
3) Is this chassis model worth salvaging or should I find another desighn to restore?

your input would be most helpful. I have some jpegs of the sams and some color photos of the project itself if you will be needing images.

regards,


Allen

[whitelabrat]

My guess would be that a single EL84 per channel amp would be pushing a max of 6w in class A.

You could plop in a replacement OPT but it may be a real challange matching one to the old one. Perhaps you could buy one and if you don't like the results you could replace the OPT on the other channel too.

Worth restoring? Let me put it this way. You'll probably learn a lot, and you can always mod the circuit to your liking.

[parvo3]

Thanks for the advice on the OPT.
I had hopes for at least 6 watts and
that would be pushing it on those
altec 14's at high volume. Replacing
both would be my choice but I need to
know what type to replace them with.

regards,


Allen

[sorenj07]

Unfortunately, that picture is absolutely minuscule and impossible to read. Try www.imageshack.us to host it in full size.

[Tom Bavis]

You aren't likely to find an exact replacement. What is hole spacing?

Edcor makes a 8K to 16 Ohm which you could use as 4K to 8 Ohms.

Hammond 125CSE is about the right size, but has no screen tap. And it doesn't have much low end.

Triode Electronics has a guitar amp replacement that will probably fit, but won't have much low end (probably less than the Hammond).

[parvo3]

We learn new stuff every day! I was afraid to overload my
jpg allocation and get kicked off! Thanks for the link to
upload images.

Here's the link to to the scanned in version.

http://profile.imageshack.us/user/pa...picturewa3.jpg

I haven't learned the tiny url thingie just yet but I hope this will work.


regards,


Allen

[parvo3]

Tom,


Hole spacing is about 2 7/8 inches or 7 cm.
I appreciate the suggestions on the xformers.
I was wondering if the OPTs from the Dynaco
sca 35 would work on it. I saw them on the
triode catalog and websit from out of Chicago.


much obliged,


Allen

[parvo3]

oops! nix the sca 35 OPT idea! (Push-pull design)
Still looking for a single ended OPT with some
better bandwidth than 50hz - 18k:-)

Maybe I will have to mod this thing after all!

[Tom Bavis]

Big transformers for an SE amp... the Hammond 125DSE is that size, as is the Edcor. 50-18K is a LOT to hope for... feedback will improve the response beyond that, though it can't help if you reach transformer saturation at the low end. The Edcor will have the best low end, as it's designed for 8K impedance - using it as 4K will take the response an octave lower.

[kevinkr]

One other possibility would be to have Electra-Print make you a replacement set.

Are you sure the primary of this output transformer burned out? Can you describe the process you used to make this determination?
How does it differ in terms of dcr from the working transformer? (Is the primary truly open?)
Obviously you need to determine the cause of the failure, presumably that channel's output tube is bad as well, and probably traceable to a bad component. The output stage cathode resistor and bypass capacitor are shared between both channels. (And should be replaced along with the coupling caps and power supply electrolytics)