TSE checkout-unable to adjust 5842 voltage - diyAudio
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Old 1st July 2012, 09:57 PM   #1
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Default TSE checkout-unable to adjust 5842 voltage

Hi,

I have been a member here since 2005 but always in the background learning as much as I could, mostly about speaker building. I have had a few vintage tube amps but I always turned on my Accuphase E-303 (which I no longer have). I kept haring about SE sound and I wanted to sample it. That brought me to the TSE.

I have a TSE board set up for type 45 tubes. I am using the Edcor XPWR131 power transformer Rknize designed (thank you by the way) and the GXSE15-8-5K output transfomer. I am using a Triad (tubelab suggested) choke in place of R4.
I started the initial checkout:

1/ no tubes
Filament 2-3v
B- 236v
B+ 0v
2/ 5AR4 installed
B+ 356v
B- 238v
3/ meters @ the grid of the output tubes to grd.
Adjust R12 and R23 to -115v and -116v
4/ install 5842's w/ meters @ coupling cap leads nearest 5842 to grd.
B+354
B- 238
Both meters read 91v. Adjusting the cathode pots R9 and R20 make no change.
I slowly brought up the voltage with a variac and the meters attached to the plates of the 5842 as described. I noticed the voltages @ the plates match the B+ to about 240v then the plate voltages drop as I increase the mains voltage to 120v. B+ is then 355v and the 5842 plate is 91v. I did stop when the mains voltage was at 60v, the B+ was 179v the 5842 plates were 178v and 179v. I adjusted R9 and R20 with no effect.

In my previous adventures it has always been some simple mistake on my part so I have put it aside twice and come back and checked my work but I haven't found anything yet.

Anything ideas?

Last edited by stonehome; 2nd July 2012 at 05:04 PM.
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Old 1st July 2012, 10:29 PM   #2
jrenkin is offline jrenkin  United States
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Oscillation. That's the same problem I had. Mine was caused by the grid resistor. Fixed by putting it in.
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Old 1st July 2012, 10:41 PM   #3
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Thanks, I'l give it a go.

Everett
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Old 1st July 2012, 10:43 PM   #4
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5842 = 417A?

The grid comes out to multiple pins - each pin needs its own resistor.

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Old 1st July 2012, 11:40 PM   #5
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OK, so the grid pins are 4, 5 7, 8. Pins 4 & 5 are tied @ the tube, pins 7 & 8 are tied @ the tube. There is a cc resistor on pin 4 on the board. Pins 7 are connected to the trimmers. So I need to put a cc resistor @ pin 7 and the trimmer?
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Old 2nd July 2012, 01:16 AM   #6
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imo 4 resistors are best.

But in practice, whatever does the job.

Keep in mind this is a VHF rated tube.

_-_-bear

and fwiw, kind of a waste on an amp that is using a 45 - already a "sweet" sounding tube. No real need to "waste" a 5842 as a gain stage in a power amp, imo...
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Old 2nd July 2012, 01:30 AM   #7
jrenkin is offline jrenkin  United States
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I didn't need more than one grid block, but also check the grid leak resistor.
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Old 2nd July 2012, 04:57 PM   #8
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Well, like I said, it's usually some mistake on my part. I looked over the board again and I had 4.7ohm CC resistors for R31 and R32, apparently thats what I ordered. I had some 2.2K CC resistors I installed but the problem still persists. I can adjust the voltage from about 88v to 95v but thats it. I can tell R6 and the 5AR4 are getting hot but I haven't left it on for more than a minute.
Any ideas will be appreciated but I'll keep checking my work.

Everett
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Old 2nd July 2012, 06:09 PM   #9
jrenkin is offline jrenkin  United States
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What do you have for R8 and R19?
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Old 2nd July 2012, 06:34 PM   #10
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HI,
R8 is 120K ohm and R9 is a 1K trimmer pot.
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