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Question: Do you think documentation is adequate bearing in mind there is no actual build procedure sheet for the amps?
Everything supplied is all I need - Docs are awesome   -2 (16.7%)
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Author Topic: overtone hrm build.. need some help  (Read 17840 times)
tonym
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« on: October 27, 2009, 08:47:33 PM »
Hi I'm new so go careful  Smiley

Just finished the Overtone HRM and have no output through the preamp. Power amp is working through return.

Voltages I have (UK) are as follows, some a little off and I can't see for looking where the problem might be.

ANY help is greatly appreciated...

Voltages:

Pin     1               2              3                 4                  5                 6                   7                8           

V1     200                          1.8                                 3.1                                      0
V2     212                          1.7                                 3.1                                      0
V3     297                           57                                 3.5                                     37
V4    0                             450                319            270                442                                  0
V5    0                             450                319            270                442                                  0


OT CT 455
HT 268 if I'm checking in the right places...

Any suggestions ?  the pin 8 of zero volts looks strange on v4 and V5 but the power amp does work. Pin 1 & 8 are tied so zero on both of those on V4 & 5....
I have some dirty pictures  : see below...

note the V4-5 was taken during the build but I think its ok - shows the build...

* v1-3.jpg (225.36 KB, 2256x1084 - viewed 808 times.)

* v4-5.jpg (91.4 KB, 1350x649 - viewed 725 times.)
« Last Edit: October 27, 2009, 09:42:59 PM by tonym » Logged
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cmoore
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« Reply #1 on: October 28, 2009, 12:08:14 AM »
I assume V4 and V5 are your Power Tubes.
Pin 3 seems normal.
Pin 4 seems pretty low. Should be closer to 450.
Pin 5 should be -VDC.  Something like -45VDC.
Pin 8 should not be Zero.  Should be milli volts.  Perhaps something like .035 VDC.
Does that make sense to you?

Pin 3 is plate voltage.
Pin 4 is screen voltage.
Pin 5 is bias voltage.
Pin 8 is your plate current across what I assume are 1 ohm resistors.
Are these 6L6 power tubes?
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tonym
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« Reply #2 on: October 28, 2009, 09:09:12 AM »
Hi Hired Hand...

Yes the V4 & V5 are 6l6wgc from TAD.

Remember I can get output from the power amp by feeding the return of the loop and while I have not tested that bit in any real depth
it seems to work.  There is VERY low output from the regular hi input on the amp - just discernable.

Problem seems to be in the preamp section somewhere and I need a clue where to look.

Ill check these voltages again presently against what you have said and repost the results on here.

thanks for your help.
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tonym
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« Reply #3 on: October 28, 2009, 07:53:04 PM »
I have checked again the voltages.

They are as follows:

Voltages:

Pin     1               2              3                 4                  5                 6                   7                8           

V1     200                          1.8                                 3.1                                      0
V2     212                          1.7                                 3.1                                      0
V3     297                           57                                 3.5                                     37
V4    0                             452                319            -25                442                                  0
V5    0                             453                319            -38                442                                  0

I don't particularly get a reading on the pin 8's of the V4 and V5. It could be me - especially if the voltages should be extremely low.

I have also posted some pics of the chassis for scrutiny by anyone....

Just need a pointer where to check....

thanks


tonym

* 6L6-V4-V5.jpg (461.56 KB, 3043x2036 - viewed 774 times.)

* chassis-lh.jpg (510.43 KB, 3043x2036 - viewed 778 times.)

* chassis-middle.jpg (722.6 KB, 3043x2036 - viewed 768 times.)

* chassis-preamp.jpg (541 KB, 3043x2036 - viewed 816 times.)
« Last Edit: October 28, 2009, 07:55:18 PM by tonym » Logged
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« Reply #4 on: October 29, 2009, 02:07:25 AM »
I really have not looked at any of your pictures.  But from your chart it seems like you have B+ problems with your screens, they should be much closer to your plate readings, and you have bias problems.  Your bias voltage should not have that disparity, the two readings should be very close to equal. Also, you need to have a meter that will read milli amps between the cathodes and ground.
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tonym
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« Reply #5 on: October 29, 2009, 04:41:59 PM »
I now have bias at 34.7 and 35.3 for V4 & V5
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« Reply #6 on: October 29, 2009, 07:44:06 PM »
Quote from: tonym on October 29, 2009, 04:41:59 PM
I now have bias at 34.7 and 35.3 for V4 & V5

Is that bias voltage on Pin 5?  Those should be negative numbers.   But they will be meaningless if you cannot read the plate current on Pin 8.   You need to find out, from some of the other guys who have built this amp, what kind of voltage they have on their screens.  Yours seem very low to me, but I have never been in one of these amps.
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tonym
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« Reply #7 on: October 29, 2009, 09:46:30 PM »
Hi,

The bias voltage was measured with a biasmaster from TAD. After ajustments that is what I got on the meter - hence the reported reading from the bias master (uses sockets under the tubes to get the measurement). After adjustment those were the figures I got.

I also got on pin 8 of V4 & V5 71.7 mv and 70.8 mv respectively.

Not sure how to get everyone to read this?

thanks

tony
« Last Edit: October 29, 2009, 09:52:39 PM by tonym » Logged
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cmoore
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« Reply #8 on: October 29, 2009, 11:11:32 PM »
This is getting a little confusing.

Quote from: tonym on October 29, 2009, 04:41:59 PM
I now have bias at 34.7 and 35.3 for V4 & V5

Quote from: tonym on October 29, 2009, 09:46:30 PM
Hi,

The bias voltage was measured with a biasmaster from TAD. After ajustments that is what I got on the meter - hence the reported reading from the bias master (uses sockets under the tubes to get the measurement). After adjustment those were the figures I got.

I also got on pin 8 of V4 & V5 71.7 mv and 70.8 mv respectively.

Not sure how to get everyone to read this?

thanks

tony

Bias voltage refers to the -VDC (negative) that is on Pin 5.  But you say those numbers are positive, and that you are reading them from a "bias meter". 
Bias voltage is normally read with a DMM.
A bias meter would normally read plate voltage (pin 3) and plate current on pin 8.
What concerns me is:
1.  You are getting positive bias voltage on Pin 5. (34.7 and 35.3)
2.  You are reading approximately 70 milli amps (71.7mv and 70.8mv) and have a plate voltage of  450 volts (452 and 453).  That is pushing those 6L6 tubes really hard (about 31-32 watts).
3.  Your screen voltage just seems way too low to me.   You are dropping well over 100 volts across the screen resistors.  Can you verify the value of one of those?  I do not think you should not have enough screen current to drop more than 5 volts.
« Last Edit: October 29, 2009, 11:16:13 PM by hired hand » Logged
tonym
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« Reply #9 on: October 30, 2009, 08:50:06 AM »
I emailed nik some pics after checking the board over and over.

The FAULT was one of the relays fitted in to it's socket the wrong way around.  Embarrassed

A simple mistake that I simply could not see.

Yes the Biasmaster just shows a voltage (probably a - voltage) as a real voltage and for 6L6WGC they say 35 on the reading so I'm pretty much there on the bias I think.

The preamp now has output so I'll check the amp further now that 'relay short' has been found and let you guys know what I find next.

Actually, I'm quite happy about this build because up to now to get it all running I just turned the relay around and this was in fact my first amp build.

I am going to make a website with the whole story on there with a video of the whole build which I have documented since day 1.

Likely I'll show the voltage measurements when this amp is dead on and of course show any obstacles in the build etc.


The site is bought but not on line yet www.overtonehrm.com

Thanks for your help again...
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tonym
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« Reply #10 on: October 30, 2009, 12:28:19 PM »
Voltages:

Pin     1               2              3                 4                  5                 6                   7                8           

V1     200                          1.8                                 3.2                                     0
V2     212                          1.7                                 3.2                                     0
V3     297                           57                                 3.2                                    38.2
V4    34.5ma                    471              465            -50                466                                  as pin 1
V5    34.6ma                    468              465            -50                466                                  as pin 1

do these look better???

thanks

tony
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erwin_ve
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« Reply #11 on: October 30, 2009, 01:47:22 PM »
What are your voltages on Pin 6 with V1/2/3?
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« Reply #12 on: October 30, 2009, 02:20:01 PM »
Quote from: erwin_ve on October 30, 2009, 01:47:22 PM
What are your voltages on Pin 6 with V1/2/3?

erwin brings up a good point.
It looks like half of your pre tubes are not working.   You should have similar voltage on Pin 1 and Pin 6.
But other than that, yes, your voltage chart looks MUCH better to me now.  You did a good job of sticking with this. 
Well Done !!!
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tonym
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« Reply #13 on: October 30, 2009, 02:35:22 PM »
V1 is 216

V2 is 224

V3 is 306

all on pin 6

there was nothing originally....

 Tongue
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« Reply #14 on: October 30, 2009, 02:47:47 PM »
PS - the bias master I used is here: http://www.tubeampdoctor.com/index.php?cPath=74

does a great job on most amps I use and it's quick and fast.

By the way - thanks all you guys for the very informative help on this forum.
« Last Edit: October 30, 2009, 02:53:58 PM by tonym » Logged
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