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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 5:02 pm
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Ok as I am still learning, I am under the impression that the tubes would be labeled as :
V1 12Ax7 is the pre amp tube on the far right... V2 12AX7 middle pre amp tube.. V3 12Ax7 left preamp tube.. Power tube 2 (6L6) AKA as V4 would be the right power tube.. Power Tube 1 (6L6) AKA V5 would be the power tube on the left.. Then the rectifier tube wild be labeled V6.. Please correct me if I'm wrong..


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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 5:07 pm
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This is all being done very haphazardly.

1. First measure all AC voltages from the transformer WITH NO TUBES INSTALLED.

2. Then install the rectifier and measure all power supply voltages WITH NO OTHER TUBES INSTALLED.

3. Leave the rectifier installed and install V1. Measure all power supply voltages and all V1 voltages.

4. Leave the rectifier and V1 installed and install V2. Measure all power supply voltages and all V2 voltages.

5. Leave the rectifier, V1, and V2 installed and install V3. Measure all power supply voltages and all V3 voltages.

6. Leave the rectifier, V1, V2, and V3 installed and install V4. Measure all power supply voltages and all V4 voltages.

7. Leave all previously installed tubes in place and install V5. Measure all power supply voltages and all V5 voltages.

8. Measure all voltages with all tubes installed.

At some point in this process your fuse may blow. Note where that occurs.

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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 5:07 pm
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michaelbpuccio wrote:
Ok as I am still learning, I am under the impression that the tubes would be labeled as :
V1 12Ax7 is the pre amp tube on the far right... V2 12AX7 middle pre amp tube.. V3 12Ax7 left preamp tube.. Power tube 2 (6L6) AKA as V4 would be the right power tube.. Power Tube 1 (6L6) AKA V5 would be the power tube on the left.. Then the rectifier tube wild be labeled V6.. Please correct me if I'm wrong..


You are correct.

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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 5:09 pm
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Ok will do!


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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 5:12 pm
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michaelbpuccio wrote:
Ok will do!


You need to follow a logical, step-by-step process or you will never figure out what is wrong.

Each tube you install increases the load on the power supply. If there is a problem in a component or wiring, the fuse will blow when one of the tubes is installed.

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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 5:59 pm
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Ok in using your process I found that the fuse blows when the rectifier is in with V1 V2 V3 and V4.. The readings I found on the tubes I believe are a bit off.. As you can see in my picture there are 0VDC values where I believe there should be voltage..

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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 6:33 pm
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V1 went from zero to 31/33 volts on pins 2 and 7 after installing V3. That does not seem right unless it is a measurement error.

Pins 3 and 8 of V1 should be the same voltage (Low). 3 and 8 of V2 look wrong also.

The only tube voltages that look reasonably correct are V3.

I would say you have some serious wiring errors around V1 and V2.

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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 6:44 pm
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Ok I'll re-check that area of my build.. Thanks for your help!!


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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 8:46 pm
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Ok I have gone through everything again and have traced every wire pin and part in this build.. Everything is in the right places and I even compared the mojotone and weber schematics and layouts.. The only thing it can be now is an issue with how it's grounded.. Is there a better/best way to do this? Also, I found that weber and mojotone wire their power capacitors differently. I'm using the mojotone method.. Don't think it would make a real difference. Next is the input jacks.. Is there a better visual explanation of wiring them in? I also think this is an issue because I must not have them wired in correctly..

Mojotone
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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 9:14 pm
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michaelbpuccio wrote:
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Just to be sure, "B" does not go to the output tube's control grids. It goes to the screen (pin 4).

OK... let's start at the beginning. Pull ALL tubes, except the rectifier. Measure the voltages at points A, B, C, D, and E. See schemo link:

https://taweber.powweb.com/store/5f6a_schem.jpg


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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 9:26 pm
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+1

If you are only making the cap connections as shown in the Mojotone diagram, you do not have the power supply wired correctly. You need to connect them EXACTLY as shown in the Weber schematic.

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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 9:28 pm
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In checking A B and C I am getting continuity through B to the 4.2k 2w resistor through to pin 6 then through the 470 1w resistor on V4 and V5..


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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 9:29 pm
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Ok I'll wire them in like the weber schematic.. Give me a few..


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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 9:30 pm
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Throw the Mojotone schematic and wiring diagram away. They flat out suck.

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Post subject: Re: Bassman LTD conversion to PTP
Posted: Wed Sep 18, 2013 9:33 pm
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michaelbpuccio wrote:
In checking A B and C I am getting continuity through B to the 4.2k 2w resistor through to pin 6 then through the 470 1w resistor on V4 and V5..


This statement makes no sense at all.

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