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
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
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
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
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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
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.
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.
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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....
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
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
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.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....
Best regards!
Good find! If your output transformers were salvaged from the radio in the schematic you can build a nice EL84 PP amplifier, even following that schematic for the amplifier part. (Did the amplifier work before you dissembled it?) Some good amplifier schematics were already mentioned, but also check diyAudio for the “El Cheapo” amp. Additionally, Dave Gillispie has nice PCBs that are upgrades to the Dynaco SCA35 that I have built and really enjoy.
Daves Store: Dynaco SCA-35 ST-35 EFB Upgrades and Restoration
The output transformers are most likely around 8k primary impedance, and obviously do NOT have UL taps. Check the transformers for continuity, at least, before investing effort. You could also verify the transformer ratio if you are up to following instructions on the web for procedures to check transformer ratio.
The 2x230 Vac power transformer is perfect for a EL84 PP amplifier. That will give you close to maximum power with fixed bias, but can also be used with automatic bias, like in your schematic, for around 10 watt output.
No, vice versa. As I said before, the EL84 may perform like the EL41 under certain circumstances. Maybe that the ECL86 shows less microphony, as it is a very much newer development (one of the most recent consumer tubes in Europe) than the old EL41 from the beginning of the 1950ies.
Best regards!
Best regards!
Interesting to see the EL41 mentioned. It's a rimlock base so a bit out of the mainstream. It's a descendant of the EL33 and EL11 but not as good sounding as either of those. Sounds quite a bit like the KT61 (used in the Leak TL10 amp), but with a slight edge to it. I tried out all these tubes as drivers. An EL33 PP amp would be nice, and something I intend to build one day. But all this is going rather OT.
I never tried the amp before disassembling so that is unknown. I will need to check the tube's and transformers. that they are not shorted or have discontinuities.
Rebuilding the amplifier part of this amp seems feasible, but I'm not entirely sure on where i need to cut the signal chain open to allow for a normal line-in voltage level without adding to much complexity for a first build.) wouldn't it be better to start with an amp that uses a 12ax7 as preamp and then two EL84 in PP?
thanks
At the start there was the EL3 and later on EL3N with new cathode technologie (Miniwatt).The EL41 is the rimlock version of the EL3N.
Mona
Looks very nice, PP transformers for the EL84.
The power transformer is a little problematic.The rectified voltage is to high,in the original circuit they loose 24V by using that for the heater of two pre-amp tubes.If you replace the diodes by a tube rectifier all is well again.But most tubes has 5V heater not present on the transformer.Can be fixed with a serial resistor or two single diodes with 6,3V heater.
Mona
At the start of all those indirectly heated 9 watt power pentodes with comparable gm was the AL4. Even prior to this one were the directly heated RES964 and AL1 and the indirectly heated AL2. All these three had much lower transconductance, though.
Best regatds!
I measured the power transformer (voltages were also labeled on the trafo)
all voltages were measured unloaded
2x 130V (measured was 140v) (I misread the voltage on the schematic)
6.3v 2.2A (measured 6.69v)
6v 2.1A (measured 6.3v)
6.3v 3.1A (measured 6.71v)
I also measured the OT winding ratio and impedance by applying 6.22v (loaded) to the primary side:
the ratio to 8ohm is about 29 and the impedance is about 6.7k
so what can I do with those components?
A Push Pull output transformer with 6.6K primary is pretty standard for EL34, so I'd suggest that's the way to go. The EL34 is also good in triode. Speaking of all the older tube types, you could use an EL33 as a driver tube, sounds very nice. Something I'd like to try out since I have some. But I guess you'd probably want to use a more standard tube, like 6SN7. Or I guess you could try some 9 pin ones since you have some.
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