dsl 401 no sound

[Enzo]

178 and 336? Both sahould be about the same. 336v on pin 1 tells me that side of the tube is not conducting.

Look CLOSELY at V4 from the top side. Each 12AX7 tube should have TWO little orange glowing heaters. Are BOTH of them glowing in V4?


Touching pin 2 of V4 SHOULD make hum out your speaker. That it does not indicates a problem right there. And the super high voltage on pin 1 agrees with me.

[T-bone]

hi again enzo,,,

i see mate,,

178 and 336 are the readings im getting mate
336v on pin 1 and 178 for pin 6
changed valves a few times both heaters lighting up,, and same readings mate


not conducting eh? .......so... .if the voltages on grid are 5-6 volts,,
voltages seem correct for heater,,,,yes?

soo....should i look @ certain componants from pin 2 towards ground?
or,, if pin 1 isnt conducting,, wouldnt you assume tube is faulty,, ive replaced tube as ive said,,,,,, ok,,, maybe ill check for faulty resistors from pin 6 though HT line?

lol,, please tell me if i sound like a dickhead, as fun as this is, i realise im still trying to get my head around what the voltages on the tube pins are suppose to be!


ONCE AGAIN I APPRECIATE THE RESPONSE AND HELP.

Thanks In Advance

[Enzo]

I didn't say the tube was bad, just that it was not conducting.

Pin 1 has B+ on it. That means R110 is probably intact. VOltage is getting to wherever you took the voltage reading.

What if there is a broken pin in the tube socket?

Pull V4, look down from the top and measure voltage at pin 1 of the socket - remember the pins count the other direction from the top. Is B+ there? That female pin could be snapped off inside the socket between the solder pin and the female grip for the tube pin.

Now power down, measure resistance from both pins 3 and 8 to ground from up top. 3 adn 8 are wired together on the circuit board. Are they showing zero ohms from 3 to 8 up top? And do both show about 22k to ground? Now pin 2. Does it show about 1 meg to ground?

And of course eyeball V4 socket closely for a bent or sprung female pin.

Your low voltage on 3/8 of 34v means about 1.5ma is flowing. That looks to me like only one side worth of current. I could be wrong.

[T-bone]

reply with thanks again.

gday enzo,, and thanks again for you intrest..

ive Pulled V4, and measured voltage at pin 1 of the socket from the top. defenetly B+ there. after your last comment, what ive done is to clean all female grips on all tubes with a small triangle dremil dimond bit, then pinched them together slightly for a better pin hold. i then did a continuity test on all solder to pin and grips,, ok,, so they are clean recheckd all previous voltages,, no change,,
then powered down, measured resistance from both pins 3 and 8 from up top,, and down bottom ( female grips ) . and they are showing zero ohms...

then from 3 and 8 to ground up top, and bottom....And they show both about 22k to ground?
(still dont know how you saw that ,,,, ive a lot to learn)

then i did pin 2.to ground.. it shows about only 180 kohms to ground?

so, the low voltage on 3/8 means one side worth of current you say,, cool,, let me try to think this out,,,,,,, ?.
does that take us back to pin 3/8 power side ,,,, or ground side that may be an issue???

soooo ive checked the resistors 114, 113 & 112 that connect to ground? they are good,,

so if pin 2 is getting correct voltage,, but its no conducting properly,, ,,,,,,,,,,,,,,,,,does that mean the draw side isnt doing its job?,, i mean,, is that where i need to have a gander???

look forward to your replies mate,, really gives me a boost,, and direction as well of course,,


learning and living!!

[Enzo]

Look at the schematic. Pins 3 and 8 are wired together, so we checked to make sure that was the case. Then they are connected through R112 (470 ohms) and R114 (22k) to ground. SO it was not that hard to decide there should be about 22k - to be technical 22,470 ohms - from 3/8 to ground.

The two grids, pins 2 and 7, each have a 1Meg resistor to the 22k, so I expect each to show about 1meg to ground - technically 1meg + 22k.

180k doesn;t sound right to me. I don't see any parallel paths, so that leaves me with :
R109 not correct value
C93 shorted or leaky
COntamination or solder bridge on or around socket

[T-bone]

reply with once again ,,, thanks

bloody hell,,, once again,, lookin at scematc, its official,, im an idiot!! it really is obvious,,,,, duh!

thanks for picking me up on that once again mate,,,,

109 resistor,, 1meg,,, is fine out of circuit and the 22nf cap reads 16.9 nf out of circuit,, not to say that when voltage is applied , it wont leak,,
dont know why they would be fine out of circuit and read fine in circuit , assuming resistance laws ..


will replace cap anyway,
socket seems to be clean and tidy, you think i should

check also for faulty componants around socket, down to ground line.??

thanks in advance enzo,,, ps i want to marry your brain!

[Enzo]

Just not sure why you woulpd read that 1M resistor as 180k. Just unsolder the cap and see if the reading changes. We may be chasing a wild goose, but the numbers don;t seem right... Does the tube alter the resistance reading? And we are taking all resistance readings with power off, right?

[oc disorder]

G'day , 'spose she's a bit hot in Queensland at the moe..............

"there was no sound injecting a signal to fx in
have tried pin 1 & 6 of v4, slight buzz issues from speaker,, voltage readings fom those pins are 178v from pin 6 & 336v from pin 1"

Pin 1 has B+ on it. That means R110 is probably intact.

"178 and 336 are the readings im getting mate
336v on pin 1 and 178 for pin 6 "

Your low voltage on 3/8 of 34v means about 1.5ma is flowing. That looks to me like only one side worth of current. I could be wrong.

R111 100K?????????

"sooo,,, is it the signal path we need to look at?
10mhz oscilloscope,, maybe you can give me an idea where to start?"

Effects return perhaps?

Attached a simplified diagram.
Redrawing a simple version of the section you are working on often helps.

[T-bone]

hi and thanks

been away a couple days,,, back now and read your replys,,, thank you soooooooooo much for seeng this through with me,

enzos quote " 180k doesn;t sound right to me. I don't see any parallel paths, so that leaves me with :
R109 not correct value
C93 shorted or leaky"

i pulled c93 like you said enzo,,,

did some testing,, and still got 180k from pin 2 of pi tube,, replaced c93 22 nanno with a 27 nano i had avalible,,, and replaced both R114 & R109 with the same ohms,, but 1 watt instead of half watts


and BINGO,,,, WORKING AMP.. BUT.............. IM GETTING A BUZZ THROUGH AMP NOW,,, SOUNDS JUST LIKE A BAD GROUND SOMEWHERE,,, COULD IT BE THAT THE REPLACEMENT PARTS NEED TO BE THE CORRECT HALF WATT RESISTORS,, AND 22NANO CAP? I WILL REPLACE ANYWHAY AND SEE... SOOOOOOOOOO CLOSE EH YOU GUYS ROCK!!!!

IVE REBIASED TO 900 MILLIVOLTS,, PLACED A HEATSINK ON TOP OF BR1 AND HOPE THE REPLACEMENT PARTS TO THE CORRECT VALUES DO THE TRICK ,, ...........

ANY THOUGHTS ON BUZZ

IF YOU GUYS WERE CLOSER ID BUY YOU A BEER


WARM REGARDS

[oc disorder]

Hi T-Bone
The wattage of the resistors nor the slight deviation in the cap value won't create the "buzz".
More likely a bad ground/solder joint or perhaps the two filter caps in the DC heater smoothing C78 & C73 - 10,000uF 6.3 volts ...10 or 16 volt ones more common to buy.
When you said in the first post -
"replaced main cap as the previous one was beginning to bubble"
I presume you meant C32 100uF 450 volts?
The other main ones in the HT feed are C42 22uF 450v ,C41 22uF 450v,
then after passing through R79 (1K) the HT 4 uses C61,C60 & C59, with V1 using C66 and C68
all of them being 10 uF 450v.
If you pull out V1 does the buzz go ?
My gut response would be to change C78 and C73 and check the ground point of those is healthy!
Then (assuming the buzz goes when V1 pulled) change C66 and C68 to make sure V1 has everything going for it, ie smooth supply.
I find there is a small unavoidable buzz on high gain settings anyway in these
amps.

[Enzo]

The original problem was that the output was very weak. So you couldn;t hear the buzz that was probably there all along. Now that the amp is working, you can now hear the buzz.

[oc disorder]

As fate or luck would have it I've just had a DSL 401 dropped off with blown heater fuse - burnt screen resistor etc .. played till the o/p tubes burst!
What I was going to point out was that the footswitch and the internal speaker jack sockets have an grounding star washer/terminal on them.
These and the front pots are the grounding points to the chassis for the amp.
You can see inside where tape has prevented paint spray or over spray from covering the bare chassis.
Make sure these are clean and the nuts on the sockets are tight which should help prevent faulty grounding .
Likewise the front panel and the pot nuts provide more grounding.
Just thought these minor details may add up to the buzz problem.

[T-bone]

hi and thank you all

hi guys,,, thanks a billion for the help ive recived from you on this amp,,,,fantastic response to my prob,,, as it is now,, the amp is purring away happy as, after i found the exact same thing you were talking about,, bad earth on footswitch connection

once again please recive my full thanks and will talk about another issue i have in a new post

warm regards

[kjb400]

I just wated to say a big thank you to Enzo and OC Disorder for all the great technical advise on this thread. I had the same problem with my DSL401 and using this thread I was able to determine that the plate resistor R110 (82K) was open causing my problem. I substituted with what I had on hand from an old TV a 75K 1/2 watt. I hope that doesn't stress anything else.

I do wonder why it went open in the first place. It doesn't appear burnt either.
Anyway, big thanks.