EL84 tube amp build, how to start?

[Jones880]

Hi I'm Jona and tube amplifier building is all new to me, so please bear with me.

I have always had the dream of building a tube amplifier for regular llow level music playing, so some time ago a received some older tube amplifier radio's. From them I sourced

2 mains transformers, 4 output transformers
and the following tubes for preamp with socket:
12AU7: 5
12AX7: 3
12AT7: 1
ECC85: 2

and then 4 EL84 tubes with socket for the power amp

So now comes the question. How would I go from here to build an amplifier. I have found some schematics using these tubes but I don't know which one I can use with my transformers.

So I think at first I need to know what type of transformers I have to continue?

Also should I go for a class A setup with the EL84 or use them in class AB.

How can I test the tubes to see if they are working.

Thanks in advance.

PS: I also got these tubes if they would be useful:
6AU6, 6BA6, 6BE6, ELC86, 6AB9

[oemcar]

Looks to me like you have the tubes for single ended (SE) or push pull (PP) design. Need to know about the transformers- what voltages and amps windings from power transformer (PT), and impedances from output transformer (OT). Then a design using what you have may be advised.
I've built 3 different EL84 PP amp designs, finally settled on which one I like the best- it's been fun learning experience. Some of my first questions were answered here about feedback polarity-lol.
Jim

[Anchan]

Transformers are a big question if you're set on using the ones you have. But the amp that I really fell in love with many years ago was a Dynaco St-35, which uses el84's. Smallish and simple amp, and you can find many kits and schematics. It's got a certain magic to it. You can also look into Tubelab on this forum which is a fantastic resource with a great community. Both PP and SE designs are available there

[andyjevans]

Push Pull EL84s are a sweet sound with the usual 8K output transformers. If yours are less than that like 6.6K, consider something like EL34 instead. The Musical Machine is a nice circuit and so is Baby Huey. Musical machine is 6V6 but should work with EL84 as well.

6V6 Musical Machine Power Supply Problems

EL84 Amp - Baby Huey

The EL84 has plenty of gain so you only need 2 stages - more than that is unnecessary, though you'll find plenty of 3 stage designs from back in the day which personally I would pass over unless the middle stage is a concertina phase splitter. If you have sensitive speakers you can use the output tubes in triode with no overall global feedback.

[45]

Originally Posted by Jones880

PS: I also got these tubes if they would be useful:
6AU6, 6BA6, 6BE6, ELC86, 6AB9

ECL86, pretty much like EL84. So anything you are going to do with the EL84 you will be able to do with ECL86.
The latter has 2 devices inside: 1 triode which is basically 1/2 12AX7 and the pentode which is almost like the EL84. So if you have 4 of these you don't need anything else....
Only practical difference with EL84 is that the pentode is specified for lower plate dissipation but this is not a problem because you don't need to run it hot to get some 8W in pure class A or 13-14W from Class AB1, both push-pull. Output transformer can be the same as most EL84 amps with 8K plate-to-plate.
EL84 and ECL86 are both among my favourites but if I had to pick one I would go for the ECL86.I have my workbench amp which is a PCL86 SE. The PCL86 is like the ECL86 but has 16V heater instead of 6.3V. The amp has got just 1 tube per channel for over 2W power (triode mode). Super simple, great sound. I built and optimized it around the Mission M73 speakers that are some very nice sleepers....

[Jones880]

Thanks already for the quick answers. I think I wil try to find out what transformers I have first before deciding on SE or PP

any tips on how to measure them if I don't have a part number?
also any tips on how to check if the tubes are still functional?

[Ketje]

If you could tell from witch radio/amp the transformers came from will help alot.
Mona

[Jones880]

I did find the schematic for one of the Amp's i salvaged (attached)

it seems like the power transformer has 2x230V output with a center tab and there are multiple 6.3v outputs for the heaters of the tubes. I have no idea about the impedance of the OTs but they have a center tab at the primary side and different tabs for different impedance (4Ohm, 8Ohm, 16Ohm and 32Ohm) speakers

[Kay Pirinha]

Originally Posted by 45

ECL86, pretty much like EL84. So anything you are going to do with the EL84 you will be able to do with ECL86.
The latter has 2 devices inside: 1 triode which is basically 1/2 12AX7 and the pentode which is almost like the EL84. So if you have 4 of these you don't need anything else....
Only practical difference with EL84 is that the pentode is specified for lower plate dissipation but this is not a problem because you don't need to run it hot to get some 8W in pure class A or 13-14W from Class AB1, both push-pull. Output transformer can be the same as most EL84 amps with 8K plate-to-plate.
EL84 and ECL86 are both among my favourites but if I had to pick one I would go for the ECL86.I have my workbench amp which is a PCL86 SE. The PCL86 is like the ECL86 but has 16V heater instead of 6.3V. The amp has got just 1 tube per channel for over 2W power (triode mode). Super simple, great sound. I built and optimized it around the Mission M73 speakers that are some very nice sleepers....

The ECL86 pentode shares it's data and ratings with the EL41, the EL84's predecessor. It's a 9 watts pentode and not bilaterally interchangeable with the 12 watts EL84. The EL84 can replace the EL41 if the cathode resistor is adapted. EL41/ECL86 do feel better with other OT's than the EL84's. And the PCL86 is the 0.3 A/14 V heater version of the - expensive - ECL86.
Best regards!

[45]

The ECL86 will perform like the EL84 in real life. The EL41 is not up to the same task as I have always found it to be quite microphonic.
Sorry, yes it's 14V heater...