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 Post subject: Thor is complete!!
PostPosted: Sat Jan 29, 2022 11:23 pm 
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Just finished soldering! Of course UPS came at the last minute today so had been waiting on the grommet and 4.7k resistor all day. But it’s done. Fired it up, Voltages looked good. Popped tubes in and….wasn’t able to bias it. Just going to drop it off at my amp techs and have him give it the once over. If it needs different value resistors or something I don’t have them anyways. Darn was hoping to crank it rock some riffage, but guess I will have to wait a bit.


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 Post subject: Re: Thor is complete!!
PostPosted: Sun Jan 30, 2022 10:37 am 
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"Voltages looked good"...including the bias supply voltages?

When trying to bias, did you set your meter to VDC (NOT mA)?

Was the problem not being able to get the tubes in the correct bias range?

Did turning the bias pot change the bias supply voltage or did it just stay there?

Was the amp in the "play" position (not in standby)?

Sorry for all the questions, but if you got this far and your voltages look good, then it could be something very straightforward.

If you are not getting negative voltage to your grids, it could be because the under-the-board wire is loose or poorly connected:

Remove all the tubes, and turn on the amp (follow safety procedures as outlined in the manual). you can leave the SS rectifier module in place, although for this test it doesn't matter. You can leave the amp in standby mode.

Set your meter to VDC measurement, ground the negative lead to chassis and using the positive meter lead check the voltage at the junction of the 27K resistor coming from the bias pot where it attaches to that corner turret on the board where the 15K resistor is located (by the 2 bias caps). It should be around -35 to -40 VDC, it might be a little more negative than expected because the transformer is not loaded down right now.

Now turn the bias pot to see if you have a change in negative voltage. If you do, that's good.

Now check the voltage at the bias feed end of 220K grid leak resistors. There's two of these, and they are connected together with a buss wire right in front of your middle and bass pots. You should get the exact same voltage there as you did when you checked the voltage at the 27K/15K junction. If you are not getting negative voltage there, I suspect your under-the-board bias supply wire came loose or you have a poor connection. Sometimes under-board wires come loose while soldering components/wires to the board after the board has been mounted (I've learned this the hard way).


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 Post subject: Re: Thor is complete!!
PostPosted: Sun Jan 30, 2022 12:13 pm 
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Alright so I just checked and I am getting -37 at the 27k/15k resistor and -38 at both the 220k resistors.
And when I move the bias pot it changes. Last night when I went to bias tubes. The first 6v6 was already at the max voltage with the pot all the way down (23ma) and the 2nd 6v6 was at 49ma. But maybe I had the wrong setting on my multimeter? I think I am confused somewhere. When I check pin 5 of the 6v6’s I am getting -31 to each.


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 Post subject: Re: Thor is complete!!
PostPosted: Sun Jan 30, 2022 12:48 pm 
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Are you plugged into a lightbulb limiter? If so, that could be the problem. Plug directly into the power source and bypass the limiter.

Are you probing the red probe to pin 8, and the black probe to ground when taking the reading (in other words, you are checking the voltage across the 1 ohm resistor)?

Your meter must be on VDC. The number you get can be converted to mA using Ohm's law. So if you get 25VDC, then this is 25mA.


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 Post subject: Re: Thor is complete!!
PostPosted: Sun Jan 30, 2022 12:54 pm 
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Also, to properly bias, you will also need your V4 and V5 plate voltages (pin 3). You might as well write down pin 4 (screen grids) for V4 and V5 as well.


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 Post subject: Re: Thor is complete!!
PostPosted: Sun Jan 30, 2022 1:04 pm 
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No limiter. At pin 8 on the first 6v6 (my multimeter on dc mv setting) I am getting 22 mv. But pin 8 of the 2nd 6v6 I am getting 40mv (v4). I am getting 390v at both pin3 of v4 and v5. On pins 4 I am getting 392 on each one


Last edited by Snoopzilla on Sun Jan 30, 2022 1:14 pm, edited 1 time in total.

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 Post subject: Re: Thor is complete!!
PostPosted: Sun Jan 30, 2022 1:11 pm 
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do you have a 1-ohm resistor between pin 8 and pin 1 on both V4 and V5?

Can you post a pic of both V4 and V5....its hard to see V5 due to the impedance selector.

Also, you could swap tubes (V4 and V5) and see if the voltage follows the tube, or stays on the socket. That will help determine if its a tube problem or a socket/wiring problem.

I and many others have had some quality issues with JJ tubes, especially their 6V6S.


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 Post subject: Re: Thor is complete!!
PostPosted: Sun Jan 30, 2022 1:31 pm 
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Yeah I don’t care for most JJ tubes, Ehx are my fave 6v6 so that’s what I have for this one. I just swapped tubes and got the same result. Here’s a pic with the impedance selector out of the way.


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 Post subject: Re: Thor is complete!!
PostPosted: Sun Jan 30, 2022 1:55 pm 
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"Same result" do you mean the 42mA bias stayed with the socket (V5)?
If its not the tube and its the socket, then I'm running out of ideas.

Voltages look good on pins 3 and 4.
Your negative grid voltage looks good.
Maybe something to do with the 1-ohm resistor on the "faulty" socket but I am not sure. Given that pin 1 on V5 has two wires and the resistor lead, its possible the extra soldering time on that pin may have overheated the tiny resistor. I don't know.

You could try a different method of determining plate current to see if you arrive at the same numbers. However, these other methods are generally a little dangerous compared to the method of using the 1-ohm bias-sensing resistor.

https://ampgarage.com/forum/viewtopic.php?t=10330

The Trinity support forum doesn't get a whole lot of attention these days. You may want to see what the guys over on the hoffman amps forum can tell you. They are all extremely knowledgeable and very active on the forum.
https://el34world.com/Forum/index.php?board=13.0


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 Post subject: Re: Thor is complete!!
PostPosted: Sun Jan 30, 2022 2:16 pm 
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Thanks for the help. This is why I figured I would drop it off at my
Amp techs. But then you got me thinking that I was just measuring something wrong.


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 Post subject: Re: Thor is complete!!
PostPosted: Sun Jan 30, 2022 2:24 pm 
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Given you have near-identical plate and screen voltages between V4 and V5, and identical grid voltages on pin 5, it seems the problem must either be the tube or the cathode pin 8. Maybe the connection between the 1-ohm resistor and ground. Or the 1-ohm resistor. Or the socket itself. Possibly one side if the OT is significantly higher resistance than the other?? idk.

A common error is to set the meter to mA when doing bias measurements across the 1-ohm resistor. I've done that myself, which is why I suggested that.

Good luck with getting it sorted out. I'm sure the 2204 circuit through 6V6's will sound incredible.

Report back when you get it up and running. Your lead dress looks great and it seems like a very clean build.


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 Post subject: Re: Thor is complete!!
PostPosted: Sun Jan 30, 2022 3:14 pm 
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Thanks. I definitely will report back. Super pumped for this amp. I have a 6v6 powered Or120 clone my amp tech built me a couple years ago and I think they will complement each other well.


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 Post subject: Re: Thor is complete!!
PostPosted: Tue Feb 08, 2022 9:05 pm 
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Alright he got it biased. Guess he just went
Over all my solder joints around bias circuit/power tubes and I guess I missed the phase inverter cathode. I pick it up tomorrow. I also missed connecting pins 4 and 5 on the preamp tubes (in the layout it just looked like the wire passes over pin 5 to pin 4, but after staring at it for awhile I totally see it now, so he left that little bit for me to do.


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 Post subject: Re: Thor is complete!!
PostPosted: Wed Feb 09, 2022 9:58 am 
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Glad you were able to figure out the problem and hopefully you can get it finished off this week.


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 Post subject: Re: Thor is complete!!
PostPosted: Wed Feb 09, 2022 9:15 pm 
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We’ll picked it up. Soldered my pin 4 to pin 5 on the pre amp tubes, plugged it in and went to play and can barely hear it fully cranked. Ugh. I did do some chopsticking and got excited as I found a loose connection, it did help but it’s still not right


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 Post subject: Re: Thor is complete!!
PostPosted: Thu Feb 10, 2022 9:17 pm 
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Sweet!!!! Just got it working finally!!! Was driving myself bonkers going back over all my solder joints and nothing was still happening. Decided to check the layout one more time and realized I totally missed a jumper on the board and Blammo. This is definitely louder then my other amp.


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 Post subject: Re: Thor is complete!!
PostPosted: Thu Feb 10, 2022 11:11 pm 
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That’s awesome! Don’t keep the neighbours up.


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 Post subject: Re: Thor is complete!!
PostPosted: Fri Feb 11, 2022 10:05 am 
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Cool! How does the high gain sound on this amp? The preamp is similar to a JCM800 right?


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 Post subject: Re: Thor is complete!!
PostPosted: Fri Feb 11, 2022 2:26 pm 
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Jag_Jones wrote:
That’s awesome! Don’t keep the neighbours up.


Luckily we live near the airport so all the houses around here have sound insulation, so haven’t had a complaint yet


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 Post subject: Re: Thor is complete!!
PostPosted: Fri Feb 11, 2022 2:39 pm 
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PharmRock wrote:
Cool! How does the high gain sound on this amp? The preamp is similar to a JCM800 right?

Sounds amazing. I left all the bright caps in and I almost wish it was a little brighter, though my cab/speaker is on the darker side. Need to get a new one for this amp (BBQ grey wolf in my current cab). I wouldn’t say it’s super high gain, to me it definitely nails that JCM 800 sound. With the cold clipping options on the back makes for some more versatility. The stock setting has more gain and the slo setting definitely cuts gain a bit and smooths it out a little. I may pick up one of those hot mod evo v2. (You plug it in v2 and it adds another tube/gain stage, without having to modify anything)


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