Mission Stock 5E3 can I do this????????

[bgood]

Stock build from Bruce's kit. Want to experiment but not desolder and mess around inside.

Can I substitute 6l6s and a different recitifier without mods? If mods are needed what would they be on the standard kit/tranny set up.

[tubeswell]

To run a 5Y3Gt or a 5AR4, you need 2A rating on the 5V PT winding. To run a 5U4GB, you need a 3A rating on the 5V PT winding.

To run a pair of 6L6s and a couple of 12AX7s for a 6L6 powered 5E3, you need 0.9 + 0.9 + 0.3 + 0.3 + (lamp - say 0.3) = 2.7A (say 3A) rating on the heater (6V) Pt winding, and about 150mA minimum (some people would say 180mA) rating on the High-Tension (325-0-325) winding.

You also need a PP OT rated at about 20W that you can run the load resistance at between 3k2- 6k6 (say 4k). You can run a smaller OT, but it will saturate sooner.

[bgood]

Great Info. I wish I had the technical skills to figure out if I have that going on in the amp. I don't know what the trannys are rated at and I guess if I had some skill I could measure/calculate those values and see for myself but I just don't have the background. I painted this kit by the numbers and it produced a great amp but I'm afraid I didn't learn much in the process. I'll try to do some reading on how I might figure this all out with a multimeter and some math

I have noticed that Bruce posts here occasionally so - Bruce if you see this, please ring in on it since I'm thinking you know the answer based on the way you spec the kit. I've sent email with no response.

[Chris / CMW amps]

Originally Posted by bgood

Stock build from Bruce's kit. Want to experiment but not desolder and mess around inside.

Can I substitute 6l6s and a different recitifier without mods? If mods are needed what would they be on the standard kit/tranny set up.

Try contacting Bruce, he knows the ins and outs of those kits and the used transformers.

The 1st thing to make it happen is using a 10 Watt 250-270 ohms resistor for the cathodes from the 6V6s.

When using MM transformers and the correct resistor I can use 6L6s and other rectifer-tubes in my 5E3-style amps.

[bgood]

And found the following info:

PT
heater 6.3v/4A - good
5V/3A good for 5Y3GT thu 5u4GB - good
680v/130ma - not sure on what the implications are here

OT
MA-59 OT
15w 8000 ohms primary - may need higher rating
with 8/4 ohm secondary - could I run the 8 ohm speaker via the 4ohm output and get away with it? Any impact there?

cathode resistors are 220 ohm

Based on the responses it looks like I DON'T have what I need in a PT/OT and looks like i would want to change out the bias resistors. Is that fair to say?

[tubeswell]

Originally Posted by bgood

And found the following info:

PT
heater 6.3v/4A - good
5V/3A good for 5Y3GT thu 5u4GB - good
680v/130ma - not sure on what the implications are here

Should be ok - with a 5U4G you get about 411B+, and assuming a 250R cathode resistor giving about -30V bias, you'd have (380V cathode to plate) about 60mA on each 6L6 at idle (120mA in total) for a dissipation of 23W with a few mA left over for the pre-amp tubes (As long as they are 6L6GCs - and not 5881s/6L6GBs). Of course you'd ideally bias 5881/6L6GB tubes to be idling at about 17W (which would require a higher value cathode resistor). (NB these assumed voltages are all estimates for the purpose of dead-reckoning)

Originally Posted by bgood

OT
MA-59 OT
15w 8000 ohms primary - may need higher rating
with 8/4 ohm secondary - could I run the 8 ohm speaker via the 4ohm output and get away with it? Any impact there?

Should be ok with 4R speaker plugged into an 8R secondary (giving 4k Pr Z) - will saturate sooner than a bigger OT.

Originally Posted by bgood

cathode resistors are 220 ohm

Based on the responses it looks like I DON'T have what I need in a PT/OT and looks like i would want to change out the bias resistors. Is that fair to say?

You should grab a bunch of 10W resistors - 220R, 250R, 270R, 300R, 330R and that way you have experiment with different biasing. The tubes ideally should be biased at 70% of maximum dissipation rating to run in Class AB1, abut anything between 55% and 85% should work okay (the higher you idle the tubes the more robust they would need to be - like winged-C 6L6GC)

[bgood]

Originally Posted by tubeswell

Should be ok - with a 5U4G you get about 411B+, and assuming a 250R cathode resistor giving about -30V bias, you'd have (380V cathode to plate) about 60mA on each 6L6 at idle (120mA in total) for a dissipation of 23W with a few mA left over for the pre-amp tubes (As long as they are 6L6GCs - and not 5881s/6L6GBs). Of course you'd ideally bias 5881/6L6GB tubes to be idling at about 17W (which would require a higher value cathode resistor). (NB these assumed voltages are all estimates for the purpose of dead-reckoning)

I'm going to give this a try and I'll have to get a resource to show me where to measure these voltages. then I can experiment as you suggested to get close to 17W


Should be ok with 4R speaker plugged into an 8R secondary (giving 4k Pr Z) - will saturate sooner than a bigger OT.



You should grab a bunch of 10W resistors - 220R, 250R, 270R, 300R, 330R and that way you have experiment with different biasing. The tubes ideally should be biased at 70% of maximum dissipation rating to run in Class AB1, abut anything between 55% and 85% should work okay (the higher you idle the tubes the more robust they would need to be - like winged-C 6L6GC)

Will do.

Thanks again!!