10,000 Series NOS Build

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Probably Loud
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10,000 Series NOS Build

Post by Probably Loud » Fri Oct 09, 2015 4:56 pm

Soooooooo....

I just finished a mid 1967 Superbass/Lead/Whatever build and I am excited as hell to use it but I have mondo high voltages on pin 3 of all the power tubes. I initially did not check them and threw in a shitty old set of tubes just to test it and I was playing it and it sounded decent. No where near as loud as my Superlead reissue however :scratch: but good none the less.

Now I noticed the bias range was -50 to -62 or so, so I changed out the Iskra 68k and put in a 47k from the bag of components from Valvestorm and that brought it down to a range closer listed in the Owl instructions. However the range was still not the -30 to -50 as listed which I can't understand.

More importantly after dumping in a fresh set of Mullards they became wicked hot and redplated at idle, so I shut her down quick. I took out the tubes and checked the voltages and it sits at 540 ON PIN 3!!!! Is this not crazy ass high? I just want to play this damn thing already and make a ton of noise. Help a mang!
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Probably Loud
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Re: 10,000 Series NOS Build

Post by Probably Loud » Sat Oct 10, 2015 11:20 pm

Also I now have no bias voltage at the end of the 27k resistor or at the bias lug on the PT. Jesus christ why am I so inept???

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Re: 10,000 Series NOS Build

Post by Roe » Sun Oct 11, 2015 7:36 am

measure AC voltage in the bias circuit. then measure dc voltage after the rectifier, the 27k resistor etc
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Re: 10,000 Series NOS Build

Post by neikeel » Sun Oct 11, 2015 11:11 am

Build looks neat, bit too far away to see anything useful. Now for some questions.........

Depending on the PT manufacturer and your wall voltage 480v to 510v is the correct range.

Who's PT are you using?

What is your wall voltage, what selector are you hooked up to?

What do you measure your heater voltage in v.a.c. to be?

How are you measuring your output tube current - mV measured across 1 ohm resistors?

If your tubes are not drawing current you will have high voltages on pin 3, then when you adjust the bias and the tubes start drawing current the voltage will decrease, and you will need to recalculate:

17.5/plate voltage = maximum draw at idle.

Do not put your new tubes in until this is sorted. :thumbsup:
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Re: 10,000 Series NOS Build

Post by Probably Loud » Sun Oct 11, 2015 1:15 pm

neikeel wrote:Build looks neat, bit too far away to see anything useful. Now for some questions.........

Depending on the PT manufacturer and your wall voltage 480v to 510v is the correct range.

Who's PT are you using?

What is your wall voltage, what selector are you hooked up to?

What do you measure your heater voltage in v.a.c. to be?

How are you measuring your output tube current - mV measured across 1 ohm resistors?

If your tubes are not drawing current you will have high voltages on pin 3, then when you adjust the bias and the tubes start drawing current the voltage will decrease, and you will need to recalculate:


17.5/plate voltage = maximum draw at idle.

Do not put your new tubes in until this is sorted. :thumbsup:
The PT is a Marstran 1203-80

Wall voltage is unknown but I am assuming around 120-125

The heater voltage is 3.20 vac

I have yet to measure the output tube current

I realized later last night that I forgot to hit the ac/dc button on the multimeter which is why I was reading no voltage from the bias tap lol. :shrug:

EDIT: I just checked the resistors on the power tubes and I have 0 current draw apparently. Like I can play it but theres like hardly any volume at all. It would be like if someone was playing an a youtube video off there phone.

I hate that it is a long weekend! I want someone to look at this thing and get it roaring...

Here are some better. non shitty, photos!

http://imgur.com/a/C7LOs

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Re: 10,000 Series NOS Build

Post by neikeel » Sun Oct 11, 2015 2:13 pm

I cannot see any glaring errors.

With your output tubes out when you measure the -ve voltage on pin 5 of each output tube does it vary when you turn the bias pot? If not check your bias pot wiring, it looks unusual layout from the picture but I presume you checked all the connections are correct?
Neil

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Re: 10,000 Series NOS Build

Post by Probably Loud » Sun Oct 11, 2015 2:49 pm

It does vary. I don't have the numbers off hand but its within the range of what should be acceptable (-30 to -50).

The OT is a 1202-132 for future reference. I also switched to the low voltage taps, which brought the plate voltage down to 500 volts.

Here is a better picture of the bias pot. The middle leg is attached to the bus wire between the 2 caps and there is a piece of bus wire attached to one of the bias caps itself. The other leg is obviously attached to the (now) 47k resistor.
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Re: 10,000 Series NOS Build

Post by Probably Loud » Sat Nov 21, 2015 11:34 am

Well I have had it working for the past many weeks, but it doesn't sound quite right! It doesn't seem loud enough and cleans are hardly how I figured them being. The volume barely comes on before 2-3. Could this be some sort of a phase invertor issue?

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Re: 10,000 Series NOS Build

Post by neikeel » Sat Nov 21, 2015 6:17 pm

Still struggling to see an error, I presme all the under board links are present and correct, no wires trapped under standoffs?

Both channels the same?

What happens with the tone controls?

Have you made a voltage chart yet?
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Re: 10,000 Series NOS Build

Post by Probably Loud » Sat Nov 21, 2015 10:06 pm

I dime both channels and jump them to get enough overdrive. I have not sat down and gone through the voltages yet since I got the amp back from the tech. He didn't do a great job tbh. He kept referring to it as a JTM45, so I am not going to use him again.

I emailed Lou from Rappoli amps to get a good voltage chart for the preamp board locations, but have yet to get anything a week later. :(

Maybe I will have to go see him.

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Re: 10,000 Series NOS Build

Post by Probably Loud » Sun Nov 22, 2015 11:48 am

I used a voltage chart as a reference and my voltages all seem low on V1-V3 :(

I checked the positive ends of the power board filter caps and they are seem legit to me, as well as the Erie on the preamp board.

FucccckkkkkkkkkkkkkkKKKKKK!!!!!!

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