First post - TubeDepot 5E3+ Tweed build and stuff

[Dave H]

Center tap to plate on the output transformer is 215Ω and 216Ω respectively. The output transformer is dropping about 11V per tube. Both Cathodes (to ground) are 27.3V. All measurements made with a DVM to ground. Pin 3: 413V, Pin 4: 384V, Pin 5: 0.16V; Pin 8: 27.3V

Then we have a measure for the plate current of 11/215 = 51mA
Plate dissipation is (413-27.3)*0.051 = 19.7W!

[pdf64]

As mentioned previously, a 5Y3 of vintage manufacture should be used with 6V6; a 5R4 may be ok.
Only use the GZ34 with 6L6 type power tubes. Otherwise the HT (and hence power tube dissipation) will be excessive.

[Justin Thomas]

To add what pdf said, my experiencce has been that with smaller-bottle tubes that run at really high voltages and are cathode-biased way hot, that trying to keep raising the cathode resistor to get them biased safely is not the best-sounding way.
I know data sheets ×were written in a mindset that didn't take "guitar amp excess" into consideration, but maybe the fact that NONE (that I have seen) list data for a cathode-biased tube that's at it's maximum ratings or above. They'll give it for fixed bias quite often, but not cathode biss. Maybe there's something in that... They knew performance would suffer.

Personally, I think to take a small amp like a 5E3 & run it like that kinda defeats the purpose of a 5E3 in the first place.?.?.?
I love TD for parts but kinda wonder what they were thinking...

I also noticed another thing: on the schematic they show the power tubes as "6V6GC." I've never heard of such. It's either 6V6GT/A or 6L6GC. So, is it JUST MAYBE AT ALL THE TINIEST BIT POSSIBLE that they intended this amp for use with <6L6GC> power tubes?????

Justin

[Mike6158]

Yep, the numbers show high bias too. The gizmo and the real numbers match pretty nicely but the bias is way too hot. I had calculated power but I've found if I get too many lines of text in my post they won't post so I kept it short. There is an option to use fixed bias but the default is cathode bias. I just checked my stash of rectifier tubes and I have a 5Y3. It's a new JJ 5Y3S. On the up side, I got to see the getter flash when I powered it up (it's the little things in life that make me smile). Plate voltage dropped from 388 to 344. Plate current (used the gizmo to save time) was 42.6mA. Plate dissipation is 14.6W which is .6W over 100%. So it helped. The tubes are JJ 6V6S's. I don't know what TD had in mind but I just noticed that the rectifier is called out on the schematic as a GZ34/5AR4. Do you suppose they meant to use the GZ34 in fixed bias and the 5AR4 for cathode bias. I'll look thru the manual but I don't recall seeing that anywhere. Lets see if this will post...

[Mike6158]

To all who brought it up - Thanks for the heads up on the GZ34. I heard you but honestly... I was struggling with why a reputable vendor would miss a key component like that so badly. Justin - I don't know much about speakers but could the 50 in the Jensen Mod 12/50 8Ω part number on the speaker mean 50W? Maybe they did have the 6L6 in mind? I don't know... I I still want to get the amp down to 10W-12W before I put anymore time on it. I'll wait to read thoughts on the GZ34/5AR4 note that I added in the post above this one. Maybe I need a 5AR4?

[pdf64]

5AR4 is the North American name for the GZ34 (european), the same tube can be called either.
I suggest to look for a vintage, used but ‘tests good’, warrantied 5Y3 on ebay etc.
I guess that with 6L6 and a GZ34, fixed bias and reconfigured OT, if the PT and OT are beefy enough, may get 35-40 watts.

[Mike6158]

pdf64- Thanks for the heads up. I was hoping that I had "discovered" TD's logic behind the circuit. I don't know how many of those kits were built but I'm going to bet long time amp builders didn't buy them and at some point the amps will eat their output tubes. I'm almost positive that I have a few NOS 5Y3's in my larger tube storage box back in Texas (those things are getting scarce unfortunately). I'll check (and bring it back with me) this weekend. For now the amp will stay powered off. I'll update the thread when I install the NOS 5Y3 next week. To all that have helped- Much appreciated. I have to finish putting my Silvertone 1484 back together so I may be posting about it. I've got 4 other amps that I want to build (all use Hoffman's eyelet boards). All Fender. One is a Bandmaster clone for a friend. One is a Fender Twin Reverb clone. One is a fender Bassman clone for me and at the moment... I can't remember what the 4th one is. Doesn't matter, it'll be awhile before I can get to it. I may be out of forum prison now. I like this place. I'd like to visit more often.

When I get home I'll check what PT and OT they supplied. Might be worth configuring to go either way (fixed or cathode / 5Y3 or GZ34)

[Chuck H]

Being only .6W over max diss in a cathde biased amp isn't a deal breaker at all. There are many amps that behave similar. Granted most use el84 type tubes, but some do use 6V6's. It's not really uncommon. The 5e3 isn't indicated as a "class A" amp as far as I've read, but I do know that it's idle bias is typically in that range. Keep in mind that the amps bias will cool a bit when conducting signal because the cathode voltage will rise and the plate voltage will drop. This is the reason many class A cathode biased amps are actually a little over 100% dissipation at idle. The extra current is determined "safe enough" I assume by the designer and it helps center the bias when the tube is actual conducting signal.

Also... JJ 6v6's are notoriously able to handle higher operating voltages and currents. Even though the tube data sheet just regurgitates the vintage spec of 14W max plate diss you may not actually be at max for the JJ tube.

I say... If the tubes aren't red plating and the amp sounds good then just leave it with the 5y3 you have in there. You're done At least you can use the amp without any major concerns until you get a vintage 5y3 that may drop a tad more voltage. Like I said, if the amp is working well why trouble about it.

[Justin Thomas]

I still wanna know what TubeDepot means by a "6V6GC."


Jusrin

[Chuck H]

I still wanna know what TubeDepot means by a "6V6GC."


Jusrin

Maybe the same thing JJ means by 6V6 in general

[pdf64]

Now that the plate dissipation is reasonable, there's no reason not to use your 5E3, life's too short not to enjoy the fruits of your labours

It may be that the JJ 5Y3 has the same characteristics as a vintage 5Y3, I suspect it's the Russian ones that got the bad rep for modern manufacture ones.

FYI the standby switch is a klodge, it's a 'hot switching' type which promotes early failure of rectifier tubes; standby switches have no benefit for this amp circuit anyway, so best not to use it.

And under the 'design max' rating system (by which 6L6GC have a 30 watt plate limit), it seems that all 6V6 have 14 watt plate limits.

[Dave H]

I still wanna know what TubeDepot means by a "6V6GC."

"GC" means Glass Container

[Enzo]

That is a popular misconception spread by Aspen Pittman. The G all by itself means glass. The C means third revision. For example the 6L6 was a metal tube. The 6L6G was a glass version. Then there was 6L6A, then 6L6B, and finally 6L6C.

[Justin Thomas]

I see that winkyface, Dave H!

That's for 6L6. I have never heard of a 6V6GC. Only 6V6, 6V6G, 6V6GT, & 6V6GTA. Have had my hands on each. TD is asking for a tube that doesn't exist. Kinda like Mullard reissuing their own 6L6GC.

I think it's possible that some folks could get mislead. Not tgat tgey can't ask questions, but mistakes can be honestly made. Do we know which part is the typo? Is it the V or the C? An error either way can either burn out your tubes (plugging 6V6 into a 6L6 circuit) or the heater winding (6L6 in a 6V6 amp).

Maybe I should call TD & ask what the chicken is going on...

Justin

[Chuck H]

Not tgat tgey can't ask questions, but mistakes can be honestly made. Do we know which part is the typo? Is it the V or the C?

I think it's the g