No worries, I fixed them. There is something strange happening with putting gallery photos into the posts. I'll look into it.
Be careful of those electrolytic capacitors. If no bleeder resistor is present the caps may still be fully charged from power up...
Much like PL84/EL86 except for heather voltage/current.
Those tubes are designed to run at lower anode voltage and higher anode current than the EL84.
Since I can't see anything looking like an output transfo, this amp could have been designed as an OTL driving high impedance (around 800 Ohms) loudspeakers. This was a "Philips" speciality 😉
Yves.
Thanks for the warning. About every manual or post I read from Tubes always stresses out the danger of tubes.Be careful of those electrolytic capacitors. If no bleeder resistor is present the caps may still be fully charged from power up...
There is an output transformer which is not in the photos. It has a 8 ohm and 16 ohm output (which is written on the transformer). The speaker that came with the Bell & Howell projector was a 8 ohm 5 watt speaker. It had 2 output terminals for additional speakers (with no markings to state watts/ohms,etc)
Some more pics.
Click here for a bigger image http://www.diyaudio.com/forums/gallery/showphoto.php/photo/7074
This is the backside of the pre-amp with one ECC83 Tube. Click here for a bigger image http://www.diyaudio.com/forums/gallery/showphoto.php/photo/7073
And this is the side of the ECC83. Click here for a bigger image http://www.diyaudio.com/forums/gallery/showphoto.php/photo/7072
Click here for a bigger image http://www.diyaudio.com/forums/gallery/showphoto.php/photo/7074
This is the backside of the pre-amp with one ECC83 Tube. Click here for a bigger image http://www.diyaudio.com/forums/gallery/showphoto.php/photo/7073
And this is the side of the ECC83. Click here for a bigger image http://www.diyaudio.com/forums/gallery/showphoto.php/photo/7072
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No. He is reading from the tubes data sheet. the 6P value is likely grid-cathode and has nothing to do with any capacitor.
I can see the photos. I can even guess the function of most parts but really the first thing to do is to sketch out a schematic. It is nearly impossible to work on something lie this unless you have a schematic. It's not hard. There are not so many parts. un-plug the power, make shure the caps are al discharged and remove the tubes. Now with an ohm meter you can measure from (say) one end of a cap or resistor and see which tube pin it connects to draw it on paper. After a few hours you will have a very messy schematic.
You might be able to re-build it without understanding it fist but without evening knowing the function of a part it's hard to know what values might be reasonable.
No need to rush, take the time to trace it out and draw a neat diagram
Thanks ChrisA for the advice, and I will make sure to discharge the caps with a proper bleeding resistor.(Dont like bang sounds or worse shocking )
Is it also necessary to to measure out all the resistor's value with the multimeter? (by taking them out one by one of course and note down where the original position of it was first) Or can I re-use the old resistors? All the values is visible on the caps (including the old tantalum style caps), so it is fairly easy to replace them with new ones.
For now I am still busy tracing the tracks on the PCB (like you said ChrisA, it takes time) Once I am done, I will post the rough schematic, or even better, do it in Eagle Layout Editor for some suggestions on what's the best way to re-construct the amp.
Will keep you guys posted.
Is it also necessary to to measure out all the resistor's value with the multimeter? (by taking them out one by one of course and note down where the original position of it was first) Or can I re-use the old resistors? All the values is visible on the caps (including the old tantalum style caps), so it is fairly easy to replace them with new ones.
For now I am still busy tracing the tracks on the PCB (like you said ChrisA, it takes time) Once I am done, I will post the rough schematic, or even better, do it in Eagle Layout Editor for some suggestions on what's the best way to re-construct the amp.
Will keep you guys posted.
This thing looks rusted. Well it happens... And as you prolly have noticed the circuit board is disintegrating too.
The rust you see there is from the plate it was originally mounted on, which will obviously be canned. The transformer itself is in good working order and has no rust on. The stuff you see on the transformer is a type of protection chemical. As far as the circuit board is concerned, well it is also going to the bin - only after I'm done with the schematic-. I am busy with the schematic and will fabricate a complete new circuit board. All in the making...
That's very good to hear, transformers are not cheap.
Since you are going to make a new circuit board, why bother at all copying this 60's design? There is a boatload of proven good schematics in this forum! UL/PL 84 is a little different from EL84, but with the people's help you can adapt a schematic for them. Maybe even make a new one?
Uhmmm, yes, that is a possibility, but since I want to learn how these amps work, I figured it is better to fix up this old one then to start a new one?
On the other hand, it would be nice to have a more modern schematic. You gave me some thinking to do before I start spending money and effort on this old design. I will look around more on this forum and see if I can't find an existing diagram which can save me some time (and frustration)-I was hoping initially by looking only at the datasheet that I would be able to build one from scratch, but not so straightforward, specially with the dangerously high voltages involved!!-
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Thanks Costis, I guess that is why we go on forums to get some sensible advice too!
Wessie: Since it sounds like you are up for an adventure and an education, it's probably worthwhile to empirically determine the specs for your power transformer and output transformer. Once you have the specs, you can evaluate applicable schematics on the forum for a modern design that suits your needs and ability.
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