ECL86 SE amp- help

[kodabmx]

@allen @kodabmx

thanks for the suggestions. .i will get back. is there somewhere i can upload a video.?

Youtube?

 

[DrFireBottle]

Hi guys...

So I am up to something with my leftover ECL86...
Usually i build guitar amps but this is going to be a multipurpose amp
(guitar and line) I am planning on using similar schematic to this one and modding it a little bit to look like a guitar amp...

Is it a good idea for a leftover parts that I have on my bench waiting ages?
(ECL86, sockets, UL41 ol' OT, 220v PT, EZ80)

Well.. tell me what you think.

 

[an2727]

Hello DrFirebottle

I would be intrested in your progress. wish you all the best. at the moment im still to find where the huge buzz is coming from when i put in the aux cable. so im going to lay all the pieces into a proper chasiss and see what happens then. I noticed the grid voltage read zero volts after i put the grid leak at 1 meg and added a 33 k grid stop. i dont know if thats the right voltage. should it not be a little negative. It was about 0.6 volts negative with the original schematic. what mods are you doing to the schematic?



good wishes!

Amit

 

[an2727]

Youtube?

yes i will do that soon as i am done with the chassis job.!!


btw what should i check with my ohm meter/DMM to see if the current/ voltages/ bias( whatever that is ..is correct?


BR

Amit

 

[kodabmx]

Grid should be around ~0V, check the voltage at the cathode and use ohms law to find out how much current is flowing based on the value of the resistor. Measure the plate voltage and you can calculate how much power is being dissipated in the tube.

Loud hum when the input isn't grounded is perfectly normal, even on most transistor amps. Blame RCA for making a connector that connects hot before ground. If it works correctly when the input is connected properly I'd say your amp is fine.

 

[Tesla88]

I've looked at your implementation on the proto board, it seems right but i suggest to check with schematic, also check for bad connections, cold solder joints, etc ...
Write here measured voltages at each tube's pins, all referred to 0V rail.

The coupling cap which goes from the plate of triode to the grid of pentode is rated at least 350Vdc ? Isn't the green one a standard 50 - 100 V rated ?

The fact your amp "eats" notes at low volume tells me your amp is possibly into some self oscillating problem, since layout is not that good and it's running without negative feedback, it's easy to get some oscillations above the 20kHz

 

[an2727]

Grid should be around ~0V, check the voltage at the cathode and use ohms law to find out how much current is flowing based on the value of the resistor. Measure the plate voltage and you can calculate how much power is being dissipated in the tube.

Loud hum when the input isn't grounded is perfectly normal, even on most transistor amps. Blame RCA for making a connector that connects hot before ground. If it works correctly when the input is connected properly I'd say your amp is fine.

Thanks i will check this!!!

 

[an2727]

I've looked at your implementation on the proto board, it seems right but i suggest to check with schematic, also check for bad connections, cold solder joints, etc ...
Write here measured voltages at each tube's pins, all referred to 0V rail.

The coupling cap which goes from the plate of triode to the grid of pentode is rated at least 350Vdc ? Isn't the green one a standard 50 - 100 V rated ?

The fact your amp "eats" notes at low volume tells me your amp is possibly into some self oscillating problem, since layout is not that good and it's running without negative feedback, it's easy to get some oscillations above the 20kHz

Thanks for the suggestions. i started reading up all over the web and got the idea that the amp is oscillating but wasnt sure as it sound fine on louder volume. but yes. it did make a motorboating sound initially if touched my finger the tip on the aux cable after plugging it in. i do not know what to do. shall i change the resistor values. all the 1k's down to 800 Ohms.?? i read somewhere that many resistors of the same kind in a circuit may make the circuit oscillate. .

im sure if i was to ask someone to hook up a scope to the amp hes gonna see a horrid waveform. but the distortion sounds nice .i have now changed the circuit back to the one in the schematic. still on my chassis build.i used aluminum sheet 2mm( its what i had).

will get back soon as im done.!! thank you!


and thanks a lot guys for taking your time to helping me out!

BR

Amit

 

[an2727]

here is the sound test video link...

YouTube

 

[an2727]

Measurements:
1)triode
Anode(pin9) +175 vdc
grid (pin1) -0.5vdc
cathode(pin2) +1.5 vdc

2)pentode
grid (pin8) -7vdc
cathode( pin7) 1.9 vdc
anode/plate (pin6) +250vdc
screen(pin3) +249vdc

now the AC voltages ( which I just checked anwyays)


pin 1 /grid 1.v ac
pin 2 1.6 v ac
pin9/plate 2.2 v ac

pin8 2 v ac
pin7 1 v ac
pin3 18 vac h

These values are with the schematic as posted( no mods)


Please let me know whatever you can gauge from this data


BR
Amit

 

[Alllensoncanon]

Have you check the ECL86. One, the Penode section Cathode at 1.9V bias is way too low. With a 5K load, it should be closer to 9V and an IP of 35mA. Your Ip is closer to 9mA per measurements. The signal gains are also way too low for both Triode and Pentode. With a -7V grid charge up at pin 8, looks like may be a lots of electron are trapped between the Cathode and Anode.

aka: If all the connections and measurement are correct, my guess is your ECL86 is not good.

 

[an2727]

Allensoncanon

Thanks

I have 15 of these ecl86. they are unused NOS.Made by BEL in india on philips machinery way back in early 80s for TV. Could it the whole lot is bad.? how do i check a tube? and what is the best way to check if my OPT is still good. i once shorted the circuit coz my DMM was still on current measurement mode.! but that was after these measurements.

thanks!

Amit

 

[an2727]

btw the amp plays really loud i wonder if it can do that if the current was low like 9ma. im going to have to check the values once again

 

[Tesla88]

Measurements:
<snip>

Are your measures refered to Ground ?
The grid of your pentode should be at 0V volt, whike cathode should be at 8 - 9 V ..

Also, are your AC readings with signal applied to input ? You can't have only 2.2V AC at triode's plate with 1V AC input at grid!



I would check connections or better if you start rebuilding from zero

 

[an2727]

Hello
Yes i have to recheck after a rebuild from scratch and put it all in metal box too. The readings were in reference to circuit ground.( the circuit ground then connects to the ground wire coming from the wall socket). there was no voltage seen between ground and neutral at the wall socket.
1 im going to rebuild with a different layout
2. star ground and then running a ground wire to chassis ground from there.
3. ground the central metal hub in the tube socket( it has one). had not done this earlier.!!
4.Move the power supply caps away from the tube. keep the wirewound resistors in the PS section away from the PS caps.
Maybe i would just replace all the wirewounds with another kind.
5. Change the value of the coupling caps
6. Connect 10nf caps from pin 7 and 3 to ground. its supposed to kill oscillations . I read this mod for ECL SE amp somewhere on a german site.
thanks for your input.!!
BR
Amit
.

 

[Tesla88]

I would suggest reducing the pentode g1 resistor, the datasheet states a 500k max , you use a 680k here, try 470k or 330k

 

[an2727]

Hi..
thank you! i will try that,
btw how does one manage to destroy an ecl 86 by improper wiring or wrong selection of resistor values?
i have 150 ma glass fuses. can i use them to save my OPT. where inn the circuit cud i place them?
BR
Amit

 

[Tesla88]

Tubes tolerate a little stress so exceeding maximum ratings is sometimes ok, my suggestion is not damage related, grid leak resistor is used to give a reference to ground. Since you were getting some voltage across this resistor, while you should read 0V across it, despite i'm pretty sure is all about a wiring mistake, your tube can be a little gassys so i would try reducing grid 1 resistor to limit the effect of grid leakage.

Improper wiring in a tube circuit can surely damage the tube, a fuse is better than nothing. Is it a fast acting fuse ?
You can put it on the B+ line , after the HV capacitor

 

[an2727]

Tubes tolerate a little stress so exceeding maximum ratings is sometimes ok, my suggestion is not damage related, grid leak resistor is used to give a reference to ground. Since you were getting some voltage across this resistor, while you should read 0V across it, despite i'm pretty sure is all about a wiring mistake, your tube can be a little gassys so i would try reducing grid 1 resistor to limit the effect of grid leakage.

Improper wiring in a tube circuit can surely damage the tube, a fuse is better than nothing. Is it a fast acting fuse ?
You can put it on the B+ line , after the HV capacitor

Hello

Sorry i have been away on a work trip. I will put the fuse in there, in the mean time..i think i found the problem... my primary of the OPT was partly burnt out or open... it gave me the distorted sound at lower voltage input notes i think... the DCR went from 315 ohm to 475 to 800K and with it then no sound any more,... i think may have destroyed it when i measured with my DMM still set to current and tried to measure voltage..( absent minded stupidity)... i am going to wire up another transformer and come back here and let you guys know.... in the mean time what is ur opinion if the voltage is 310vdc instead of 250 vdc which is required in this circuit as b+??


BR

Amit