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EL84 tube amp build, how to start?
EL84 tube amp build, how to start?
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Old 24th November 2020, 12:29 PM   #1
Jones880 is offline Jones880  Belgium
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Default EL84 tube amp build, how to start?

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
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Old 24th November 2020, 01:48 PM   #2
oemcar is offline oemcar  United States
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EL84 tube amp build, how to start?
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

Last edited by oemcar; 24th November 2020 at 01:51 PM.
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Old 24th November 2020, 01:57 PM   #3
Anchan is offline Anchan  United States
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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
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Old 24th November 2020, 02:14 PM   #4
andyjevans is online now andyjevans  United Kingdom
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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.

Last edited by andyjevans; 24th November 2020 at 02:19 PM.
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Old 24th November 2020, 02:32 PM   #5
45 is offline 45  Italy
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Quote:
Originally Posted by Jones880 View Post

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....
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Old 24th November 2020, 02:33 PM   #6
Jones880 is offline Jones880  Belgium
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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?
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Old 24th November 2020, 03:12 PM   #7
Ketje is offline Ketje  Belgium
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If you could tell from witch radio/amp the transformers came from will help alot.
Mona
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Old 24th November 2020, 03:16 PM   #8
Jones880 is offline Jones880  Belgium
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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
Attached Files
File Type: pdf hfe_national_sa-52h_schematic.pdf (676.6 KB, 104 views)
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Old 24th November 2020, 03:18 PM   #9
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by 45 View Post
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!
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Old 24th November 2020, 03:31 PM   #10
45 is offline 45  Italy
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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...
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