That thru hole is for a chassis stand off, which would connect AC ground to the top plate.
jeff
to me your amp seems normal, when you touch the input with test lead, the lead acts as an antennae and pick up hum....
just input music and see what happens....enjoy, do not worry too much...
just input music and see what happens....enjoy, do not worry too much...[/QUOTE]
IT WORKS ! ! !
Probably it was working well from the start, but didn't make correct input connections and there was an antenna effect.
Here's a video : YouTube
Now it's working very well.....
Next steps : balancing channels, building a case......
But above all, DEEPLY THANKS to all people that answered .....
Along this time when I was looking hopelessly to the amp, answers from helping people even if only encouraging, have been of great help.
Thanks again.
IT WORKS ! ! !
Probably it was working well from the start, but didn't make correct input connections and there was an antenna effect.
Here's a video : YouTube
Now it's working very well.....
Next steps : balancing channels, building a case......
But above all, DEEPLY THANKS to all people that answered .....
Along this time when I was looking hopelessly to the amp, answers from helping people even if only encouraging, have been of great help.
Thanks again.
Attachments
congratulations.....see, it was easy. yours was a typical newbie concern...
what is your impression of the sound?
Regarding sound impressions will make better comparisons between DCPP and TSE 300B this weekend.
The problem I see now is that on right channel there is a big voltage difference between the two 6CBA (input), probably depend on tubes...will try to switch them or change.
Thanks again
The problem I see now is that on right channel there is a big voltage difference between the two 6CBA (input), probably depend on tubes...will try to switch them or change.
Thanks again
you mean plate voltage? a voltage difference of 10 volts to me is of little concern in a differential amplifier stage...
No, the voltage difference is more than 50V
There are trimmers (pots) to adjust the voltage difference but where on left channel I've been able to adjust with a few voltage difference, on left channel best adjust still makes a 65V difference.
That's too much, I think that unless make some big error with some resistance (will check) there must something with one tube.
Luck is I have more 6CB6 to try.
There are trimmers (pots) to adjust the voltage difference but where on left channel I've been able to adjust with a few voltage difference, on left channel best adjust still makes a 65V difference.
That's too much, I think that unless make some big error with some resistance (will check) there must something with one tube.
Luck is I have more 6CB6 to try.
I also had the problem of being unable to match the plate voltages on the 6CB6s. My trouble was the cheap MP3 player I used as a signal source, one channel was putting out DC. This amp has no cap on it's input to block DC. Good Luck.
In my case there must be something wrong.
Left channel is perfect.
On right channel without input source best situation is a 60V difference between the two 6CB6, changing or swapping tubes between channels doesn't change the thing.
So must be something "hardware", thought maybe a resistor but yesterday verified values and compared channels .... all seem the same.
Will keep looking.
Left channel is perfect.
On right channel without input source best situation is a 60V difference between the two 6CB6, changing or swapping tubes between channels doesn't change the thing.
So must be something "hardware", thought maybe a resistor but yesterday verified values and compared channels .... all seem the same.
Will keep looking.
that means it is not the tubes, look for problems elsewhere such as incorrect resistor values...
A bad day...a good day....
A good day…..a bad day…
So this is what happened yesterday, beginning from the good : you'll remember I had a difference of voltage between the two 6CB6 input tubes on left channel : after trying and switching finally discover the problem, it was one of the tubes bad....changed with a couple of NOS Philips and now all input voltage are balanced...thanks Cartesian spirit....
Should had left all that way....working... stock power transf...but devil of changing things made me decide to put at work the special bigger power transf (320-50-320 instead of 280-50-280)
First error : power cables in wrong order. Checked it three times....all seemed correct....ON and...smoke and bad smell, R7 (10 ohm) bright red and C1 smoking....ARGH
Unable to see my error thought it was a bad diode....changed it and changed R7 too, only to have more smoke....until finally saw my error.
Changed power cables, all in order, amp working again.....
Wise should have been go to sleep and follow today but you know there are days..... so go on to balance power tubes (6HJ5)...I've done hundred times....
Second error : was measuring plate voltages on right channel with two multimeter, what I did was while black cables where on right channel test point, put one of the red on left channel test point, thinking nothing would happen. Result : R2 (10 ohm) bright red and left channel dead.
ARGH...again finally decide go to bed
Today put right channel power tubes on left channel, it works...so one 6HJ5 must be bad.
A little work more and find bad tube, have opened it and attached a photo, what may be that strange worm-like draw? Is that the plate?
Ordered some more 6HJ5, hope not to make more errors.....
Just to make you know...
Thanks for reading
A good day…..a bad day…
So this is what happened yesterday, beginning from the good : you'll remember I had a difference of voltage between the two 6CB6 input tubes on left channel : after trying and switching finally discover the problem, it was one of the tubes bad....changed with a couple of NOS Philips and now all input voltage are balanced...thanks Cartesian spirit....
Should had left all that way....working... stock power transf...but devil of changing things made me decide to put at work the special bigger power transf (320-50-320 instead of 280-50-280)
First error : power cables in wrong order. Checked it three times....all seemed correct....ON and...smoke and bad smell, R7 (10 ohm) bright red and C1 smoking....ARGH
Unable to see my error thought it was a bad diode....changed it and changed R7 too, only to have more smoke....until finally saw my error.
Changed power cables, all in order, amp working again.....
Wise should have been go to sleep and follow today but you know there are days..... so go on to balance power tubes (6HJ5)...I've done hundred times....
Second error : was measuring plate voltages on right channel with two multimeter, what I did was while black cables where on right channel test point, put one of the red on left channel test point, thinking nothing would happen. Result : R2 (10 ohm) bright red and left channel dead.
ARGH...again finally decide go to bed
Today put right channel power tubes on left channel, it works...so one 6HJ5 must be bad.
A little work more and find bad tube, have opened it and attached a photo, what may be that strange worm-like draw? Is that the plate?
Ordered some more 6HJ5, hope not to make more errors.....
Just to make you know...
Thanks for reading
Attachments
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That was the cathode. The "worm" is where the white oxide coating was burned away by an arc. The oxide coating is what emits the electrons. The arc was caused by a serious overcurrent situation.
The plate was the outer black element you cut away to get here. What you have left are the cathode (white thing) two grids wound with fine wire, G1 the control grid is wound on the copper rods, and G2 the screen grid is wound on the steel rods. The silver structure is the beam plates, also known as beam formers, or just G3.
I saw the same tin in the IKEA closest to us (about 80 miles) and got so wrapped up in purchasing and disassembling a broken table (cheap) that I forgot to buy one......next time.
The only other drop in replacement is the 6HD5 which is harder to find.
There is a long list of TV sweep tubes that will work buried somewhere in the thread. Most of them would require wiring the board as Pete made it and adding a plate cap. All of these are 12 pin "compactron" or "duodecar" tubes, which are not common in the EU.
I have wired magnoval sockets into one board and tried a few tubes the US 6GB5 (EL500?) will work, but is best kept below 100 watts per channel. The 6KG6 (there are Russian and European equivalents) can eat all that board can throw at it.
21LG6 and 6DQ5 (octal) are electrically similar (but not identical) to the 6HJ5.
They definitely are not pin compatible though.
(can get 21LG6 for $4 and 26DQ5 for $3 at Vacuumtubes.net and ESRC)
They definitely are not pin compatible though.
(can get 21LG6 for $4 and 26DQ5 for $3 at Vacuumtubes.net and ESRC)
Tube destruction derby 😉 THanks for the story , very entertaining , and you sure did you sensor the scotch sips in between each paragraph
Live ... again 🙂
OK, friday received 6HJ5 ordered three weeks ago (must have come to Europe by boat 🙂 )
Saturday put on all tubes, switch ON and .... good!!! No smoke
So go on balancing both channels...good ..... left it ON half an hour....check again...
Next step : music listening
OK it makes A LOT of noise, listen for an hour and sound is very good but at some point feel some hassle, like if it's too much volume (it was around 4), lower it...same sensation.
So sound is good, a lot of it, but at a certain point I don't feel comfortable.
It's not the "easy" sound I found in the other amp (TSE 300B).
Next steps :
1) check carefully channel balance again --> maybe something was out of balance;
2) change back to stock power transf (remember I'm actually using a stronger one [320 vs 280])
3) change to better speakers --> I'm still using test ones, will change to the good ones;
Once again I would like to thank all people from this forum, people who simply stops and read, someone who answers, somemore who helps....feels like a family, it's a very nice spirit.
Thanks
OK, friday received 6HJ5 ordered three weeks ago (must have come to Europe by boat 🙂 )
Saturday put on all tubes, switch ON and .... good!!! No smoke
So go on balancing both channels...good ..... left it ON half an hour....check again...
Next step : music listening
OK it makes A LOT of noise, listen for an hour and sound is very good but at some point feel some hassle, like if it's too much volume (it was around 4), lower it...same sensation.
So sound is good, a lot of it, but at a certain point I don't feel comfortable.
It's not the "easy" sound I found in the other amp (TSE 300B).
Next steps :
1) check carefully channel balance again --> maybe something was out of balance;
2) change back to stock power transf (remember I'm actually using a stronger one [320 vs 280])
3) change to better speakers --> I'm still using test ones, will change to the good ones;
Once again I would like to thank all people from this forum, people who simply stops and read, someone who answers, somemore who helps....feels like a family, it's a very nice spirit.
Thanks
