Guild 66-J questions

[jshin]

Hi, new to the forum. I've been a long time D-25M user, and now a recent 66-J amp owner.

I have a few questions about the amp, as I'm sure there are many of you who are more knowledgeable about amps than I am.

I got the amp for a steal of a price on Craigslist last week, but it appears the insides have been molested a great deal. According to the previous owner, the amp has now been made to run 6L6s and a GZ34. The power transformer's been replaced. Unfortunately, I have no idea what the specs for the power transformer are and am unsure as to whether or not this amp has been modified properly.

So I have a few questions:

Is there any way I can find out if the specs of the power transformer are fit to run 6L6's?

I understand that if you switch 6V6s for 6L6s, the 8 ohm speaker has to be plugged into the 16 ohm tap of the output transformer. Is there any way to figure out if the amp is running the 16 ohm tap?

If I were to replace the output transformer, what specs would I need to ensure that the 6L6/GZ34 tube compliment is being run correctly? Would a standard Deluxe Reverb OT suffice?

Thanks all.

 

[Fixit]

Welcome to the forum, If you can find out the part number and manifacturer of the power transformer from the part itself, it should be possible to look up the specs. 6V6 vs 6L6 should be quite different in their power requirements 6V6 pair usually will produce about 20 watts where a pair of 6L6's usually in the 40 - 50 watt range. Most of the work I do is on guitars and not much on amps, but some of our amp guru's should be along soon. Again welcome

 

[jshin]

Snapped some pictures of the transformers which might help.

The unused wires on the PT are:

red/blue, red/yellow, green, and orange.

What do you guys think? Everything setup properly?

 

[Default]

That transformer looks pretty much like overkill! :wink: Rather than changing the output transformer, I would put JJ 6v6's and maybe a 5U4 to tame the B+ voltage a bit. If you want to change the OT, get a 6.6K primary, 35 watt OT. You could use a 50 watter, but the speaker will probably need to be changed, if it's the original one.

 

[beinhard]

Hi, jshin, and welcome to LTG.

Your power transformer is marketed as a replacement part for Vibrolux so it will handle 6L6s.

I am a little unsure about the transformer wiring and unused wires.
Do double check, and compare with what the transformer label says about windings and color codes.

As to if the amp has been modded properly or not, that's hard to tell without looking closely.
There's also the question of what "properly" means in this context.
Depending on what the modder was trying to achieve, you could see things like a changed cathode resistor, conversion to fixed bias, a PI using 12AT7 .....

beinhard

 

[killdeer43]

Way out of my element here, jshin, but not so much that I can't stop by to say WELCOME TO LTG!
As you can tell already, your Guild questions will find informed answers here, so enjoy your stay. :wink:

Joe

 

[Default]

Well, you don't need 4 amps on the heater wiring for a 66J, that's for sure! I would figure that the B+ might be over 460 on that amp, due to higher wall voltage and fewer tubes in the circuit. Put a bassman-sized output transformer in there and you are going to end up with a pretty loud amp.

 

[jshin]

So I've been reconsidering replacing the OT.

Rather, I would like the amp to run 6V6/5Y3 again. As the amp is, will a 5Y3 drop the voltage enough to safely run vintage 6V6 tubes, as I've read that their maximum VDC is around 425. Also, the new power transformer shouldn't have any problems powering a 5Y3, since it can power a GZ34, yes?

 

[beinhard]

The 5Y3 actually draws slightly more heater current than the GZ34, 2A vs 1,9A.
Both are well within the 3A rating of the 5V winding of your transformer.
Sorry, no experience with 6V6. Default?

beinhard

 

[Default]

Believe I said 5u4, Beinhard?

That particular rectifier has more voltage drop across it than a gz34 and there is more than enough amperage on the 5 volt winding to handle a 5u4gb. 4 amps on the 6 volt winding is enough to install el34's and their higher heater draw.
The reason that i suggested specifically JJ 6v6's is due to their toughness. If you check the weber and hoffman amp boards, people are running JJ 6v6's in Fender Twins and the tubes shrug off the higher voltages. Since this power transformer is intended for 5 preamp tubes and 6l6 power tubes, the reduced current draw of a 6v6(22 ma as opposed to the 35-40 ma of a 6L6) is going to push the voltages higher than the desgn of the average nos tube. Maybe 460-470 volts? My Vibrolux runs at 445-450 volts B+, depending on the wall voltage.
Not sure what you mean with the "experience with 6v6" remark, but if the op wants to go back to 6V6's without changing the pt back to a tweed deluxe ot, JJ's are the way to go, imho.

 

[Default]

Jshin, if you could take the back off, and take some gutshots of it, we would all like to see what changes were made. If the first cap in the filter circuit is too geat in value,(>20 mfd, iirc) it will cause reduced life for the 5y3.

 

[beinhard]

Believe I said 5u4, Beinhard?

You did, I was responding to jshin who asked about 5Y3.
The 5U4 heater current of 3A is the rated current of the transformer, but this should not be a problem as long as the other windings have a relatively light load.

Not sure what you mean with the "experience with 6v6" remark,

That was my response to the other question jshin asked in his last post.
Your name was mentioned because I believed you could give a better answer.
You did.

beinhard

 

[Default]

Sorry for my misunderstanding. That's what I get for posting when I should be working. My apologies, Beinhard!