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That was what my friend was talking about BTW, the fact the amp has a shared screen resistor, and that now I'm running all 4 tubes on 1 100 ohm 1 watt screen resistor. He thinks I should split it up and use different values for the 6v6's and the EL's. He relaxed his position on it after a day though lol.

The PT is the exact same size. The 36 watt OT is twice the size of the 18 watter, but the pt is the same. It has a 5 volt winding which is needed. Really though, it is probably fine, because the Mercury was running just as hot. It was the fact that the tubes were drawing waaay too much current. I could probably put the Trinity back in now and it would work fine. Live and learn I guess.

We had a few sets of these 36 watt PTs with no issues. Typically, the size of the conductor inside is made heavier to accommodate the extra current being drawn for 4 tubes versu 2. Sometimes, and I can not recall in this case, they add laminations or change the lamination material to handle the extra current.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Hey Zaphod... you edited your post and it made it look like I was saying.......... You could get me in big trouble that way!! LOL

Stephen, I know the PT is fine.....now..... I might end up going back to it if I cant get these voltages straight. I'll just use the Mercury on another build.

I've got some new issues now, but I'm not tellin yet. Gimme a day or so and I think everything will be straight. What an adventure I have made this into

There's something wrong right there!


You might end up needing them, if the PT voltage rises with the reduced current draw. Note, that if you're using fixed bias (a misnomer if there ever was one), you will need to have separate adjustments for the EL84 and 6V6 tubes.


Not a good idea IMO either! That might have been the reason for your problems. Or possibly the EL84 grids weren't solidly at 0 V. But why did you say plate resistor?


I would recommend you just give each tube its own individual 1k 2W screen grid resistor. That will help everyone sleep more easy at night.


I thought it was unfair to refer to a crackhead as a moron.

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Yes, there was/is something wrong that I couldnt get the amp to cool down when in cathode bias. Heres the lowdown of what I have on it: Mercury Mag PT 315-0-315. Mercury Mag choke, 10 henry. Trinity 36 watt OT. GZ 34. I was using the big cap mod, I had 1000 uf caps on each set of tubes. The PI and the grids were stock Trinity values. I did only have one screen resistor, the 100 ohm Trinity value, for all 4 tubes. Thats a no good I guess.

I like the amp better cathode biased. I thought I wanted it fixed bias, but I was wrong. The thing is, I like cathode biased when it has the big cap mod, not when it has the normal value bypass cap.

The amp is fixed bias right now, and running 4 6v6's. I have 2, 5 watt screen resistors, one for each pair. Everything else is as I listed above. It sounds very very good like this, better than your average amp for sure. The thing is, it sounded freakishly good before. The kind of good where all my bandmates took notice, the kind of good where i was grinning from ear to ear every time I fired it up. Next week I will get the 9 pin converters, and try it fixed bias with 6v6's and El 84's. I have 2 pots, will run seperate controls for each pair. Hopefully this will get it close to where it was before, otherwise, we mst find a way to make it work cathode biased, with the big cap mod. By "we" I mean Zaphod must find a way to make it work.
Gimme a few days and lets see how the fixed bias sounds first though.......

BTW, the voltages have jumped up to 385 on the 6v6 plates, and the amp runs as cool as the other side of the pillow.......

That shows the tubes' current draw has gotten more where it should be. Probably due to the improved screen resistors. It also means you probably need to go back to the other PT, as well as maybe find some other way to drop some volts.


WTH is that for?? Seems like you sure like throwing money away on over-priced MM iron.


So go with that then.


I would personally prefer each tube to have its own 1k 2W screen resistor. But no chokes. Those just don't belong in the 18W/36W architecture, and will just make your amp feel looser.


IMO don't waste your time on fixed bias, if you prefer cathode-biased with the huge cathode cap. I reckon your problem most likely came from the screen resistor situation, and possibly also the ground reference to the tube grids was faulty for some reason.

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Great tones come in small glass jars!

As far as the current draw being where it ought to be, yep, I believe thats whats up, but why?, thats what I'm not sure of. It sure dropped when I went to the fixed bias, thats the one thing I can pin it to. I'll be honest, I cant remeber the order of things exactly, but you and the crackhead are both thinking the screen resistors are the cause, although he thinks the fixed bias is part of the reason too.

Gotta disagree with you on the choke thing, it sounds great, and improved sustain a ton. I can hold notes out like Carlos Santana with a fricken Strat loaded with Suhr Fletcher Landau's! Not a whole ton of output coming from those pickups....

Yep, gotta go back to cathode bias, or at least see how the mixed tube thing is. The amp does not sound as good now, flat out, not really even close.

No Mercury iron is a waste of money for me. If it doesnt work for this amp, it will work for another. I have Mercury iron in almost all my amps, their stuff sounds good, albeit expensive. I could have have cooked dinner on that PT, my reasoning was at least somewhat sound.

So, if when I go back to Cathode bias it still runs hot, what do you suggest? I'm not gonna mess with it too much longer though, I have learned a TON from this amp. If it still runs hot and I cant get it right, its going back to 18 watts, but with that big OT , and I'm just gonna build a JCM 800, or a 50 watt plexi next.

The point you guys dont seem to get is that I use these builds to learn. I could have the crackhead make me any amp I want, at cost, and he is very very very good. The Super Reverb/dumble ODS he built me is the best sounding amp I have ever played, and I'm old man, I've been playing for a long while. So the reason why I keep messing with this thing is purely to learn. How can I say for sure what a choke sounds like in this circuit until I have actually heard it myself? Fixed bias? 6v6's? ,Mix of 6v6's and El84s, Mercury iron? Get my point? This amp sounded great the day I finished the kit, sounded beautiful. It didnt need fixing, I just wanted to mess with it. I'm pretty close to done now though, I just want to get it sounding good and play it now, really this time.....

You guys are great too btw, I appreciate the teaching very much.

There's no logic in that - unless the grid reference (grid leak) resistors weren't properly ground-referenced for some reason. That's a common reason for the kind of problem you had. If the power tube grids aren't sitting tight at 0V in a cathode-biased amp, you will get all kinds of over-current problems.


OK, I can't argue against that.


However, you get the same quality from Heyboer at half the price. IMO with MM you're paying extra just for the name.


Give each power tube its own 1k screen resistor, and make sure those grids are solidly at 0V. Then adjust cathode resistor values to get dissipation to around 85% or 90% (with the huge cathode caps). You may have had cathode resistor values that were too low. The 6V6s and EL84s should be running with separate cathode resistors.

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I'm not so sure if he thinks Fixed bias amps are inherently more efficient or just easier to control, so far I would have to agree with the latter though, so far .....


The only problem I have with Heyboer, is that I cant buy direct from them. I have to go to Mojo to buy thier iron, and then the selection is very very limited. With Mercury, the whole catalog is at my disposal. Otherwise I would most certainly opt for Heyboer most of the time.
Later in the week I will follow your advice when I try to return the amp to cathode bias, and mixed power tube. Very unfortunately I think perhaps a certain friend of mine has viewed our thread here. I only perpetuated the use of the term "crackhead" to bust your chops, because really he said the same thing as you, it was I who mixed up the terminology. The guy is a very knowledgable and capable builder, who has been very good to me. I feel kinda bad now, this isnt the first time he has misunderstood me. I hope it isnt what I think, and I'm just being paranoid.....

So-called "fixed-bias" amps are usually easier to adjust the boas on, as its just a matter of turning a pot. With cathode-biased amps you have to swap a few different cathode resistor values to get the bias right.

BTW, I don't know how you connected in that choke, but it may also have helped caused your tubes to red-plate, if you didn't also have the usual B+ voltage dropping resistor in front of it.

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Thats why I told you about it, I figured there was a possibility... I installed it across the cap can, I removed the resistor that was on the cap can, and replaced it with the choke.

I probably lost that detail somewhere in all the information. So the screen grid voltage probably would have been too high, and with little current limiting through the 100 ohm safety resistor. Also what value did you use for the dropping resistor between the two halves of the cap can, before you took it out? It should have been about half of the value used in a regular 18W - ie 1100 ohms. When using a choke you could subtract the DC resistance of the choke from that resistor value, to calculate what value of dropper resistor would need to be used with the choke.

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wesmont, you're making progress. Good for you!

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks Coco. I have learned alot during this 18 watt exploration. When I started this build I could follow a layout/directions and solder, but I was very confused by how these things actually functioned, even with quite a good bit of research on the topic. Really its been the wrong moves I have made, and Zaphods explainations of these mistakes that actually has me at a much much greater understanding of how tube amps function. At this point, I kinda understand power sections.

An update on the neverending 36 watt build..................

9 pin adaptors are on back order at Mojo, I didnt realize this when I ordered them, I figured it out when the rest of my order arrived, but not the adaptors, which were the main reason for my order.
Went back to cathode bias.
Re-installed dropping resistor across the cap can, along with the choke.
Installed a small terminal board to aid in the installation of the screen resistors.
1000 uf caps and 300 ohm resistors on the 6v6 cathodes, might need to go 320-360
Voltage on the plates is down in the low 370's now.
Have played a couple gigs on it with zero issues..

Amp sounds great, is running very quiet, and pretty cool also. I could leave it as is and be happy right now, its really running great. Of course I will have to try the EL 84's again when the adaptors arrive though.

Good news. Would really like to hear it. Sounds like it is time for Amp Pictures & details for posting!!

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I'm holding out for the EL84+6v6 version. That one's going to sound amazing!


That voltage is somewhat on the high side. EL84s start to loose some of their magic around there. You may need to look at some way of dropping around 25V. It would also be a really good idea to take some measurements and work out what you 6V6s are dissipating.

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Great tones come in small glass jars!