5e3 hum

[Noval_novice]

Ok. So with a grid stopper of 470K and a drop in the cap before the PI from 0.022uf to 0.01uf, the distortion is much less noticeable. Sounds just about perfect now. Thanks for the help.

[Noval_novice]

On a separate note, I measure my output to be 19.2 W per tube. The Wmax of my JJ 6V6S is around 10W! Again, it sounds good, but I don't want to chew up tubes every week. Do I need to increase the shared cathode resistor?

[FYL]

What are your plate, screen and cathode voltages?
What is your cathode R?

Nearly 20W is way too much, even for rugged critters such as the JJs. You should shoot for 14W max with these.

What kind of PT, OT and recto are you using and on which mains?

There are easy fixes:

- If you use a Sovtek 5Y3GT, which is *not* a 5Y3GT but a Russian indirectly heated valve quite close to a GZ34/5AR4 when it comes to plate R and voltage drop, replace it with a real NOS 5Y3GT.

- Use a larger cathode R, say 330R instead of 250R. Or more. Tone doesn't suffer up to 470R or so.

Usually a NOS 5Y3GT and a 330R cathode R bring everything back to normal. As a last resort, you may drop 15 to 25V B+ by adding a suitable zener diode between CT and ground.

[Noval_novice]

Here's the info:

PT is Mojo761ex
OT is Mojo773
Mains is 120ish (I assume. I have not measured.)
Recto is a JJ GZ34

Voltages at:
plate 430V
cathode 25.8V
screen 0.7V

Cathode R is 250 ohms

[FYL]

Recto is a JJ GZ34

A GZ34 only drops 10V @ 100 mA and 12V @ 150 mA, a 5Y3GT 43V and 56V...

plate 430V

That's 80V above vintage spec. OK, contemporary versions run hotter but you shouldn't go above 380V or so.


If you haven't done other mods and parts subs, replace the GZ34 by a real 5Y3GT, use a 330R or 390R cathode R. Voltage should be app. 380V and diss. app. 14W. If your build is still too hot, you'll have to add dropping zeners (quite simple).

[Noval_novice]

So I borrowed a NOS 5Y3GT from one of my other amps and the plate voltage is down to 380. Plate dissipation now calculates to be around 16 Watts. I don't have any suitable resistors to swap out the cathode resistor, but will do so soon.

Does biasing the output tube hot have any (desirable) tonal qualities?

[FYL]

So I borrowed a NOS 5Y3GT from one of my other amps and the plate voltage is down to 380. Plate dissipation now calculates to be around 16 Watts.

Pretty normal.

I don't have any suitable resistors to swap out the cathode resistor, but will do so soon.

Get some 10W models if you've got enough room, they'll run cooler and the bypass cap will thank you.

Does biasing the output tube hot have any (desirable) tonal qualities?

The 5E3 runs in deep class AB1, with a very rich bias. It sounds best between 10 and 14W total dissipation (depending on the actual circuit, components and tubes used). Low diss for "hard" vintage tubes, high diss for modern versions such as the JJ you use.

Anything hotter reduces the amp's useful lifetime with no tone benefits whatsoever.

[rp]

I was gonna do a post on this but to tell you right now:

I put a new pt in my clone cause I needed 220v taps. Before I had hammond @ 350 side but like all hammonds was spitting out too much - 368V unloaded gave me 385+V on plates. I was never happy with the amp and tweaked many things. Waste of time.

New PT was custom built at 330V loaded. Gave me ~340V on plates (lower than I'd hoped, wanted 360V) old tubes of some sort, 250 cathode r, 38Ma, taking out a little for the screens about 11.5W diss. All else stock except 22mf at start and 5751 V1. Sounds sooooo amazing - Finally, after many years!

So I'm very ok with the 340V too, I can now play with 5V4 or SS pop in thing.

Seems brighter and tighter too oddly enough though opposite should true. Bit less loud. No less distorted maxed just nicer. Before couldn't handle 12ax7 in V1 - bet now no problem but haven't tried yet.

If you are unhappy try a new PT not too expensive for the 5E3.

Mission kit builders all seem to prefer lower V from my web surfing. Maybe you can get a PT from him.

[labb]

Take a look at Magnetic Components Inc. For a reasonable priced PT..I think the the standard spec for the 5E3 PT is 660 at 120 ma. This is going to give you about 385 VDC to the power tubes if you use a NOS 5Y3 rectifier. Over 400 if you use a Sovtek. MCI's 40-18035 is 580 at 120 ma. That should give you about 345 with a NOS and about 365 + with a Sovtek. I am getting ready to try a 40-18027 which is 550 at 100 ma.(I think the 100 ma is plenty for the 5E3. Should give me 330 with a NOS and 350 + with a Sovtek..Going to be fun to try anyway.

[rp]

Just a link to one post about B+ in 53E that I came across and had convinced me to go down w/ the new PT. I know nothing about Mission Bruce other than from web posts but he seems to live the 5E3.

http://archive.ampage.org/threads/4/dlx ... 5E3-1.html

[rp]

Take a look at Magnetic Components Inc. For a reasonable priced PT..I think the the standard spec for the 5E3 PT is 660 at 120 ma. This is going to give you about 385 VDC to the power tubes if you use a NOS 5Y3 rectifier. Over 400 if you use a Sovtek. MCI's 40-18035 is 580 at 120 ma. That should give you about 345 with a NOS and about 365 + with a Sovtek. I am getting ready to try a 40-18027 which is 550 at 100 ma.(I think the 100 ma is plenty for the 5E3. Should give me 330 with a NOS and 350 + with a Sovtek..Going to be fun to try anyway.

Careful not to go too low. I find getting a Pt to give you a specific plate V really hard to figure out, though my knowledge is limited.

My 5E3 is now, heyboer ordered at 330v loaded @ 125VAC, 123 VAC Wall, RCA 5Y3, rec pins 4/6 328VAC, C1 22mf 350V, 4K7 -> C2 16mf 323V, 22K -> C316mf 261V Plates 338V, SG 323V, Bias 19V w/ 250 R. Power tubes are JAN Hytrons or something with a brown base. Not sure you want to go below 340 plates - no good reason really, but seems a little too low. I lost some volume and I wouldn't want to loose any more. Maybe this info will help.

Oh... OT is supposedly a close copy or orig, got, I believe, from John Sprung - Parts is Parts in '93 - not as many options then. Reads 300 ohms to ct.

[labb]

Actually I am putting the PT in a 5B3 clone which is practically the same as a Rickenbacker M11. I got a chance to open up a M11 and measure the voltages..It measured 323 VDC on the anodes of the 6V6's, 150 VDC on the anodes of the PI (6SC7) and 66 VDC on the anodes of the pre amp tube (6SC7}. Sweet sounding amp..I am trying to set up the 5B3 just like it.

250 ohm cathode resistor and 18.5 VDC cathode voltage. That would give you about 11 watts plate dissipation per tube. Pretty close to the old 70% rule.

By the way, Bruce of Mission amps would be considered an expert by most on Fender 5E3's.

[rp]

5B3 huh, good going, now I wanna build one too! Gotta stop for a while too costly a hobby. This might interest you for that amp, I know nothing about it just something I surfed across:

http://w.mawebcenters.com/midwestspeake ... eaker.html

[labb]

That is one heck of a price for a 12" Alnico speaker. Shame I have already bought a Warehouse guitar speaker 12" Reaper..I have the 5B3 built and it sounds really good with B+ of 340 VDC. Kinda hate to be fooling with it but just can't help myself..Only problem is that one of the 6SC7's is really microphonic, Guess I will end up having to replace it with a 6SL7.

[Noval_novice]

If my plate voltage is too high, can I try to use 5881wxt tubes instead?