• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

ID tube amp kit 8 watts stereo.. unsure what tubes to use

kcroy

Member
2013-10-21 12:38 am
I acquired this DIY tube amp kit - I have attempted to ID it, but could use some help. I have limited electronics experience ( can use a multimeter for example ) but couldn't tell if this a "push pull" or other amp type just by looking.

H5mLc1H.jpg


c7ulM6l.jpg

It looks similar to this:

https://www.tubedepot.com/products/stereo-tube-amplifier-kit

My end goal is to replace the tubes, and I want to make sure I am using the correct type. In the box were 2 tubes, one I can't ID ( but looks visually similar to the ones shown on the website above ) , and one JJ ECC82.

Any insight appreciated!
 

kcroy

Member
2013-10-21 12:38 am
It should be easy to check the pin out on the valve base with the triode/pentode ECL85. Where the ECC82 comes in, is anyone's guess, unless this is a completely different kit.

Thanks for the quick reply [edit: sorry autocorrect]. I'm thinking that the ECC82 was either part of another kit, or someone jammed it in there and tried to get it to work. When you say "check the pin out" what do you mean? There are 9 pins. Or can I use a MM to check for something?

I like the link you sent. I might test this amp out, and if it is functional come up with a better box for it. I'm a bit worried about the heat of the transformers inside a closed wooden box. Would that be a fire hazard?
 
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Transformers should not get hot, warm maybe but not hot.
If you look at the pin out for ECL85/10GV8 http://www.r-type.org/pdfs/ecl85.pdf
Triode section; Pin1-Anode, 2-Grid, 3-cathode. 4-heater, 5-heater, and Pentode side; 6-anode, 7-screen grid, 8-cathode and 9- control grid.
On the circuit board pin 6 should go to one side of the output transformer and pin 8 should go to ground through a few hundred Ohms. If these are correct, it is probable that ECL85/10GV8 is correct. The next part is which valves to choose. If the voltage across pins 4+5 is approximately 6.3Volts, use ECL85 otherwise use 10GV8.
E(cl85) the E means 6,3V heaters and 10(gv8) the 10 is the heater voltage.
 
Putting valve circuitry inside a closed wooden box is just silly. The valves will be the hottest thing in there, although they can cope with some heat other components will not. Maybe not a fire hazard but it won't last very long before failing in some way.

'Check pinout' means follow the PCB wiring and see if it looks consistent with ECL85/PCL85.
 
Certainly looks like an earlier version of the "K" series judging by the resistors used. I have the K502 Kit that uses 11BM8 tubes ( similar to the ECL82 but a higher heater voltage requirement ). Need to look at what heater voltage the transformer provides to determine which type of tube is used. These kits were modded a lot. This seems to be no exception. Plenty of threads about these amps on this forum. :D

otherwise check this out :)



S-5 Electronics K-8, K-12 K-16 and K-502 DIY Tube Amplifier Kits
 

kcroy

Member
2013-10-21 12:38 am
Transformers should not get hot, warm maybe but not hot.
If you look at the pin out for ECL85/10GV8 http://www.r-type.org/pdfs/ecl85.pdf
Triode section; Pin1-Anode, 2-Grid, 3-cathode. 4-heater, 5-heater, and Pentode side; 6-anode, 7-screen grid, 8-cathode and 9- control grid.
On the circuit board pin 6 should go to one side of the output transformer and pin 8 should go to ground through a few hundred Ohms. If these are correct, it is probable that ECL85/10GV8 is correct. The next part is which valves to choose. If the voltage across pins 4+5 is approximately 6.3Volts, use ECL85 otherwise use 10GV8.
E(cl85) the E means 6,3V heaters and 10(gv8) the 10 is the heater voltage.

ok thanks, I can check the voltage. / resistance.

Putting valve circuitry inside a closed wooden box is just silly. The valves will be the hottest thing in there, although they can cope with some heat other components will not. Maybe not a fire hazard but it won't last very long before failing in some way.

'Check pinout' means follow the PCB wiring and see if it looks consistent with ECL85/PCL85.

The valves are mounted on top... or do you mean the pcb/circuits for the rest? Aren't those normally encased in something?

I think that is the earlier version of tbe K12 kit. It used 11BM8 tubes. The newer version (K12G) uses the 10GV8 tubes. I believe the circuit topologies are the same but a few resistor values are different.

Certainly looks like an earlier version of the "K" series judging by the resistors used. I have the K502 Kit that uses 11BM8 tubes ( similar to the ECL82 but a higher heater voltage requirement ). Need to look at what heater voltage the transformer provides to determine which type of tube is used. These kits were modded a lot. This seems to be no exception. Plenty of threads about these amps on this forum. :D

otherwise check this out :)



S-5 Electronics K-8, K-12 K-16 and K-502 DIY Tube Amplifier Kits

Definitely a K12M. Fairly easy to mod to sound decent. A bit bass starved though. Lots of info on the web on them. A search will turn up more stuff than you can ever read.

ok, awesome - thanks for figuring out which one it is!

The metal oxide resistors (blue) are overheating the PCB. I would get new ones and leave the leads long enough to where as the body of the resistor is 8-10mm away from the board.

How can you tell this? I will definitely reseat the resistor further away.

That was how my K502 cathode resistors were to be mounted. This pcb has been populated from below making things worse. The original cathode resistors may have overheated and needed to be replaced by the metal oxides.

Is the metal oxide resisters a mod worth doing regardless?

A circuit diagram of the 12M can be found in post 10 of this link, the circuit calls for 11MS8 tubes.


http://www.diyaudio.com/forums/tube...-k-12m-11ms8-8-wpc-pp-tube-amp-kit-139-a.html


Gio Militano has a link to his own build here


S-5 Electronics K-12M Tube Amplifier Kit

can't say thanks enough to everyone for pointing me in the right direction with this!
 

kcroy

Member
2013-10-21 12:38 am
In the first picture, the pc board is darkened in the vicinity of the two cathode resistors. This was common on the old phenolic boards used in '50s-'70s Dynaco gear, and still occurs in modern builds when insufficient space is allowed between the component and board.

ok I see that now.

Not really sure what to do with this thing. I did some research, and seems like there are a number of mods I should do - luckily this already has ceramic slots for the tubes, so I don't need to swap those out. I'll admit to being a bit intimidated by those 450v caps and the thought of shocking the heck out of myself.

Right now I have 3 other projects "on the bench" so to speak, ( some pot replacements on a sub, a MAC6100 SS I picked up cheap because the glass was shattered and left channel is having problems, and a guitar to rewire ) .

So I think this guy will sit as #4 project while I keep doing research and make sure I understand the circuitry and how to safely work on this thing.

I can't say enough how much I appreciate all the help here... I'll definitely be back when I start playing with this little guy.

I know this is a music thread, but I also have a crazy vintage electroshock therapy machine that is tube driven. That is my omega project for a few years from now when my electronic knowledge is in a better place lol.