High voltage V1 Pin1?

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Ceeya68
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High voltage V1 Pin1?

Post by Ceeya68 » Sat Sep 03, 2016 3:14 am

Please se vid link: (https://youtu.be/BlB6O7nDQi4) I have done something wrong or missed something. Amp works but it's real buzzy. Due to the high voltage I would guess. Also when I get the bias set where it needs to be my power tubes start to red plate. I'm so confused. Anybody help, Please!!! I can do more vid if need be. Thanx. P.s. I followed the instructions found on the valvestorm website for a 1969 100 watt metroamp plexi. And yes I'm new to building amps. New hobby I'm tryin to start. I can only get better I hope. That is if I don't blow myself up of burn my house down. Thanx.

danman
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Re: High voltage V1 Pin1?

Post by danman » Sat Sep 03, 2016 9:46 pm

Welcome to the forum! We will need some clear, close up pics of all areas of the amp to be able to help. I can't make out from the videos exactly whats going on. What is the jumper wire you have clipped onto the turrets for? When you are taking the voltage measurements in the video, your meter is not reading a high voltage. It appears to be showing a negative (-) voltage or reading a very low voltage. Is your meter set for DC voltage? Are you taking these readings with or without tubes?

First thing we will need is a full set of voltage readings at every socket. Black meter lead should be clipped to ground and set for DC voltage. When checking the heater filament voltages (pins 2 and 7 on power tubes, pins 4/5 and 9 on preamp tubes) your meter will be set to AC. Take these readings without tubes installed and standby switched into playing mode. Please list voltages at all pins on every socket and try to get some pics up when you can and we should be able to get you up and running.

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Re: High voltage V1 Pin1?

Post by Ceeya68 » Sun Sep 04, 2016 5:59 pm

Ok will do. Give a couple days. Thanx Much!!

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Re: High voltage V1 Pin1?

Post by Ceeya68 » Mon Sep 05, 2016 7:13 pm

Ok. Here are some photo's. There is no bias resistor at the moment because I installed a new trim pot. I did not do a very good job on the original. There are no power tubes in at the moment. The pre amp tubes are installed right now. I also undid the (PPIMV) and put the connections back to the instructions I followed. So there are a few loose wires disconnected that go to that. They up in the air and out of the way. In the previous video the amp is powered on but the main power only. Not the standby. It's in off position. The power tubes were removed and only the preamp tubes were installed. The alligator clip went to one multi meter that was on auto function. It is the first meter you see in the vid. The second meter is the one I am probing with and it is set to DC voltage in the 2 range because if I go any higher on the meter settings I do not get a reading at all. So maybe the problem is low voltage instead of a high voltage. The bias in the vid is turned all the way to -50. So cold I hope. Yes, I have pink resistor's. I get them extremely cheap through my work so I took advantage of it. I will try and get another video going of me taking the tube socket readings and board readings all lot slower and more informative. If you see anything askew for now please let me know. And Thanx!!! Much Appreciated!!!

http://s1152.photobucket.com/user/troyd ... slideshow/

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Re: High voltage V1 Pin1?

Post by danman » Tue Sep 06, 2016 7:20 pm

I cannot look att the pics right now because I am at work but i will check them tomorrow. The standby switch must be off (which would be normal playing mode) for any B+ voltages to reach the tubes. If you had the standby in the on position, that cuts all high voltage DC after switch but it does allow The AC filament voltage to heat the tubes.

In the video, your meter had a - mark next to the numbers which would indicate a negative voltage. The only place you should be reading a negative voltage is the bias circuit and Pin 5 of each power tube. This is a DC voltage and you need to see somewhere around -40 to -50 before inserting the power tubes. In most amps, this voltage will also reach the tubes when the amp is in standby mode.

I would first like to see a set of voltages at all sockets with no power tubes installed. You can leave the preamp tubes in for the measurements. List the preamp socket voltages at pins 1 and 6 (plates) for each socket. Also take a reading at pins 3 and 8 which are the cathodes. Your meter should not show a decimal point or a - sign before the number. If it does, we need to trace the B+ wiring.

Take voltages at pins 3, 4 and 5 on the power tube sockets also. Pins 3 and 4 should read between 400 and 500vdc and pin 5 should show the negative bias voltage.

Be sure standby is off and amp is in normal playing mode with no power tubes. Once we see where your voltages are at, we can figure out where the problem is.

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Re: High voltage V1 Pin1?

Post by danman » Wed Sep 07, 2016 5:06 pm

I had a chance to look at the pics for a bit. The board soldering doesn't look to bad but I am concerned about some of the preamp socket connections. From the pic, it appears that several of the solder joint at the sockets are dangerously close to touching each other. There are several bits of wire that also need to be trimmed back closer to the solder connections.

i noticed in the pics that you are missing a 47k resistor in the bias circuit. it should attach to the empty leg on the bias pot. You may have already caught that but I just wanted to mention it. Have you had a chance to take the voltage readings yet?

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Re: High voltage V1 Pin1?

Post by Ceeya68 » Thu Sep 08, 2016 12:50 am

Ok, Here is a vid with voltage readings. Hopefully I did it right. Also I did check the B+ fuse before I started and it is in a working condition. I did not mention that I had checked it in the vid. The vid is kinda long so please bear with me. Also I wanted to add that I used Classic tone Transformers. The PT is 40-18053 and the link for the spec page is: (http://www.classictone.net/40-18053.pdf) the OT is: 40-18072. Link: http://www.classictone.net/40-18072.pdf) And the choke is 40-18058. Link to spec is: (http://www.classictone.net/40-18058.pdf).
Thanx for the help much appreciated!!

Please see link for readings Vid: (https://youtu.be/MFLtAC-HAWc)

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Re: High voltage V1 Pin1?

Post by danman » Thu Sep 08, 2016 4:54 pm

Great video. It appears that you have proper incoming AC voltage to the transformer because you are getiing the proper AC filament voltages to all valves and your bias circuit is receiving incoming AC voltage. Everything after the diode in the bias circuit will be a DC voltage and it appears that you are getting a negative DC bias voltage to every power tube socket (pin 5).

What you appear to be lacking is the B+ voltage (DC) to all sockets. From you PT's secondary side you have several pairs of wires. The green ones are the AC filament wires and you should have a red pair which is for the high voltage. Could you measure each one of these red wires (AC) and list the voltage you see. Should be between 300-400v AC on each. From here the AC voltage goes to the standby switch and then on to the 4 diodes on the board and becomes a DC voltage. So you should have incoming AC to the diodes and DC leaving the diodes. The DC will now hit the filter caps and then on to the board where it meets with the 10k dropping resistors (large 1 or 2 watt resistors), the OT's primary and the choke wires. The B+ DC voltage will also travel across the board using the jumpers that you installed from turret to turret.

You are not getting any high voltage DC in your video so you must start from the beginning where the PT high voltage wires meet the standby switch and then head to the diodes. Check each part of the circuit to find out where the voltage stops. Remember that it is AC until the 4 diodes and then it becomes DC, so set your meter accordingly. Hopefully it's just a miswire at the standby or a cold solder joint somewhere. Also remember that you will not get any high voltage B+ unless the standby switch is in the normal playing position.

Could you post a link to the layout that you used so that we can follow along easier?

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Re: High voltage V1 Pin1?

Post by danman » Thu Sep 08, 2016 5:12 pm

Also keep in mind that voltages will read quite a bit higher until you have all power tubes installed and biased correctly. Once you are able find the mistake in your B+ wiring, take another set of readings at all sockets with no power tubes. The DC will read high at this point but will drop once the power tubes are in. Also adjust your bias pot for the highest negative DC voltage you can achieve once you are ready to install power tubes. This will insure that no redplating occurs as the tubes will be biased quite cold. You need to see proper DC voltage at pins 1 and 6 of all preamp tubes and pins 3 and 4 of power tubes before we can move on with installing the power tubes. These particular pins connect to the plate of the tubes and need the high voltage DC to function. Each board jumper on your turret board connects to the node where the plate resistors meet so this will help you to track the DC voltage across the board to each gain stage. The voltage will be highest at the end of the board where the DC enters from the filter caps. As it travels down the board through the jumpers to each gain stage, it gets progressively lower until it reaches V1. If no preamp tubes are installed, the voltage will stay at basically the same level across the board because there is no voltage drop across the plate resistors. With the preamp tubes installed and conducting, the voltages will fall at each stage in the preamp. It's a lot to take in but hopefully you will get an idea of how the voltage travels across the board and where to look for a mistake.

Ceeya68
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Re: High voltage V1 Pin1?

Post by Ceeya68 » Thu Sep 08, 2016 7:58 pm

Thank You! Danman, Here is the link to the instructions I followed: (http://valvestorm.com/sites/default/fil ... MP_KIT.pdf).
Also here is the link to the power transformer specs that I used:
(http://www.classictone.net/40-18053.pdf).
Here is a new video link doing PT/AC readings:
(https://youtu.be/-WNibMK3Fu0).
Thanx much for the help!! I hope I got everything.

danman
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Re: High voltage V1 Pin1?

Post by danman » Fri Sep 09, 2016 5:23 pm

Watching your last video, it appears that you are getting the proper DC (B+) voltage to the tubes. To clarify, the standby switch must be in play mode for the amp to receive DC voltage. If the switch is in "standby" mode, the power is cut to the circuit. The only parts of the amp that will see voltage will be the bias circuit and filament circuit to heat the tubes.

Could you do another set of readings on preamp pins 1 and 6 and power tube pins 3 and 4, all DC with the standby switch in "play" mode? From what I saw in the video, you are getting proper voltage but you only checked v1 and v7. I would like to be sure that every socket is receiving the proper voltage before moving on any further. Your issues may be something in the signal portion of the circuit such as a bad ground, bad solder joint, or wiring mistake at the input or output jacks.

What happens with the power tubes installed? Does the fuse blow? Does the amp sound weak? Post a video of a soundclip if it's possible. Always be sure to have a speaker cab plugged into the amp when you power up with the power tubes installed. Here is a great read on how to power up for the first time and how to troubleshoot if an issue arises...http://paulrubyamplifiers.com/info.html

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Re: High voltage V1 Pin1?

Post by danman » Fri Sep 09, 2016 5:29 pm

I'm not suggesting that you should unsolder any of the PT's secondary wiring like he mentions in the article but I thought it may be a good primer on how to check each section for proper voltages.

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Re: High voltage V1 Pin1?

Post by Ceeya68 » Sat Sep 10, 2016 2:25 am

Hello, Here are some more voltage readings as per requested. Please link for new vid:
(https://youtu.be/98aH6N-aPa8).
Wont be able to do a tube test with sound clip for a little while gotta go do work for work. I will get back to ya when I am ready to make more tests. Thanx so much for your help!!! Please let me know if something is askew with these readings. Thanx again!

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Re: High voltage V1 Pin1?

Post by danman » Sat Sep 10, 2016 5:16 pm

All of your voltage readings look great. The voltages are a little high in a few spot including the power tube sockets, but once the tubes are installed and drawing current, the voltage will settle down to under 500vdc.

You double checked a couple of pins on V1 which were showing no voltage, but that is normal. Pins 2 and 7 of the preamp tubes are the grids and should not have any DC voltage. The pickups in your guitar send a small (millivolts) AC voltage to the tube's grid, so unless you were actually playing through the amp, the voltage should read zero. Pins 3 and 8 are the cathodes, and these should be sitting at about 1v as they were in the video.

Since all voltages check out good, we will need to install power tubes next. Remember to set the negative bias voltage at pin 5 of the power tube sockets to the highest voltage your bias pot will allow. Be sure to have a speaker cab plugged in also.

You mentioned in the first post that the tubes redplate. Does this happen instantly or does it come on gradually?
Does the amp make any squealing or other odd noises? It may be a case of oscillation that is causing the power tubes to redplate. Adjusting the lead dress of the wiring can help in these cases but your amp does appear to be well laid out. Another culprit can be the wire leading to the presence pot. It is usually purple and George mentions how to route this wire in the instructions to avoid a problem. Please do another video of the power up with the power tubes installed so that we can see what is happening with the tubes. If you have a set micro clips for your meter leads, it would also be nice if you could clip onto pin 5 of one of the power tube sockets during the startup so that we could monitor the bias voltage. Any loss of the negative DC bias voltage will cause a redplating issue.

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Re: High voltage V1 Pin1?

Post by Ceeya68 » Sat Sep 10, 2016 5:59 pm

OK. Will do as soon as I get back to the house. It will be a little while. Thanx again!

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