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 Post subject: Tweed build with VRM
PostPosted: Sun Mar 01, 2015 10:37 am 
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I have been plugging away at my build. Got it together last night.

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Some "help" from Yuki.

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 Post subject: Re: Tweed build with VRM
PostPosted: Sun Mar 01, 2015 10:39 am 
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 Post subject: Re: Tweed build with VRM
PostPosted: Sun Mar 01, 2015 11:14 am 
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Having some start up problems. I think I may have fried the 5Y3 tube.

I got it all together but am having some problems. The pilot light comes on, I see the two 6V6 tubes glow but not the 5Y3, and I get no sound, not even a hum. I'm going through the circuit and trying to see if there was something I interpreted wrong.
When I added the VRM I moved the two 1M resistors from the 1 Hi inp‎uts. I left the jumper, from the resistor wire, between the center terminal and ground. Should that jumper be cut out?
‎ The VRM kit was missing the 6V 1W diode so I picked one up at a local electronics store. I did notice the wires on the diode where very tight in the circuit board holes so now I'm wondering if he sold me the right one. Is there any way to verify a diode?
I was a little confused on the shielded wire from the normal volume pot to the 2 terminal on 12aX7. So just to verify. The braid goes to ground at the pot ‎and the core wire goes from the right pot terminal to the 2 terminal on 12aX7? And the braid is just insulated off at the tube end?
I'll dig around the forum for some more trouble shooting but these are just the things I wasn't 100% about ‎and wanted to verify.

Here's some pictures,
I don't think the tube should be white on the bottom.
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 Post subject: Re: Tweed build with VRM
PostPosted: Sun Mar 01, 2015 12:00 pm 
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See how the top (getter) of the 5Y3 is white? That means the vacuum is lost and your tube is dead. Could have come that way from the manufacturer or it could have been knocked around/dropped sometime between then and now. Get a new tube!

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 Post subject: Re: Tweed build with VRM
PostPosted: Sun Mar 01, 2015 12:11 pm 
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kurtlives wrote:
See how the top (getter) of the 5Y3 is white? That means the vacuum is lost and your tube is dead. Could have come that way from the manufacturer or it could have been knocked around/dropped sometime between then and now. Get a new tube!



Thanks Kurt. I suspected the tube was shot just wasn't sure if it was a result of something else wrong or if it was faulty.


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 Post subject: Re: Tweed build with VRM
PostPosted: Sun Mar 01, 2015 2:43 pm 
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Looks faulty to me. If it was that way out of the box time for a warranty replacement!

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 Post subject: Re: Tweed build with VRM
PostPosted: Tue Mar 03, 2015 8:31 pm 
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Picked up a new rectifier tube and it's glowing. However still no sound.
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Here's my DC voltages as per the chart on page 52 of the instructions. Tested with the VRM fully up.

V1 12AY7 PIN 1 44.2 PIN 3 0.57 PIN 6 77.2 PIN 8 0.61

V2 12AX7 PIN 1 68.3 PIN 3 0.53 PIN 6 89.9 PIN 7 1.3 PIN 8 19.4

V3 6V6 PIN 3 168 PIN 4 152 PIN 8 9.2

V4 6V6 PIN 3 173 PIN 4 155 PIN 8 9.2

These are all considerably lower than the suggested voltages.
As I was testing points I would get a crackle here and there. Then a constant hum until I turned the VRM down a notch and then silence. Hum would come back when I turned the VRM back up.
Any suggestions what I should look at next?


Last edited by Tinman46 on Tue Mar 03, 2015 8:36 pm, edited 1 time in total.

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 Post subject: Re: Tweed build with VRM
PostPosted: Tue Mar 03, 2015 8:35 pm 
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All your voltages are really low

Look for a wrong resistor value or wiring error.

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 Post subject: Re: Tweed build with VRM
PostPosted: Tue Mar 03, 2015 8:45 pm 
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Not sure how or why I didn't notice this sooner. :?

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I guess I'm replacing that resistor.


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 Post subject: Re: Tweed build with VRM
PostPosted: Tue Mar 03, 2015 9:38 pm 
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That might not cause the lack of sound. Hope it does.
Check your hi AC voltage at the rectifier woth tubes pulled out. Did you connect the PT for 117 volts mains? The voltages look to be about half.
Does the VRM change the coltage at all?

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 Post subject: Re: Tweed build with VRM
PostPosted: Thu Mar 05, 2015 10:37 pm 
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As per advice from Steve I bypassed the VRM and the amp came fully alive. I'm really digging the sound of this amp. I can only imagine how much better it will be after the speaker breaks in.
I'll go over the VRM circuit in detail more tomorrow evening but am very happy the problem is narrowed down and I get to enjoy the amp.


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 Post subject: Re: Tweed build with VRM
PostPosted: Sun Mar 08, 2015 1:55 pm 
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I'm looking at the VRM circuit and the only thing I can think of that maybe mixed up is I turned the mosfet the wrong way. Maybe another set of eyes will see something. I've googled the 5R 2W resistor a couple times and don't get much. If someone can verify Green,brown,gold = the right resistor.

Here's some pictures. Please note what looks like a blue wire is in fact green and goes to chassis ground and the B+ wires are currently disconnected for bypass.

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 Post subject: Re: Tweed build with VRM
PostPosted: Sun Mar 08, 2015 3:43 pm 
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That's a 5R resistor

Make sure you got the MOSFET and Zener diode oriented correctly. That is a 6V2 1W Zener diode you have?

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 Post subject: Re: Tweed build with VRM
PostPosted: Sun Mar 08, 2015 4:14 pm 
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kurtlives wrote:
That's a 5R resistor

Make sure you got the MOSFET and Zener diode oriented correctly. That is a 6V2 1W Zener diode you have?


The guy at the store assured me it is a 6V 1w diode. I've checked the orientation a few times and unless I've flipped something in my head it is laid out right. I'm kinda at a loss. When I hook it up I get a growling hum at the full setting and my DC voltages are still cut in half. It will work if I turn the VRM down but not above bedroom volumes.


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 Post subject: Re: Tweed build with VRM
PostPosted: Sun Mar 08, 2015 6:39 pm 
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I agree - that does not look like the Zener that I used in my build....

viewtopic.php?f=11&t=3708

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 Post subject: Re: Tweed build with VRM
PostPosted: Sun Mar 08, 2015 7:15 pm 
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I didn't get the diode in my kit so went to the local electronics store. It may not be the same brand but is the same rating 6Volt 1Watt. I had went over that in emails with Steve at Trinity and he said the diode should be fine as long as it's in the right direction.


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 Post subject: Re: Tweed build with VRM
PostPosted: Sun Mar 08, 2015 9:35 pm 
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Can you read off the part number on the diode? It should be 1N____. We can confirm it is the right one.

The few times I've had a VRM not working it was a bad diode. I'd check MOSFET orientation and wiring still though.

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 Post subject: Re: Tweed build with VRM
PostPosted: Mon Mar 09, 2015 7:33 am 
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The number was against the board so while I was trying to see I snapped the casing when gently trying to get a look. I'll ensure the replacement is the right diode. :lol:

I've tried to google a 6 volt 1 watt zener diode and came up empty. What's the part number?


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 Post subject: Re: Tweed build with VRM
PostPosted: Mon Mar 09, 2015 11:28 am 
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1N4735

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 Post subject: Re: Tweed build with VRM
PostPosted: Mon Mar 09, 2015 12:34 pm 
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The board components, zener orientation and MOSFET wiring look OK to me. Make sure the B+in and B+out are correct and a good ground connection on the green wire.

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