Hi all,
I've been offered an amp, but the seller knows very little about it other than that it has 2 x el34, 1 x 6sl7 and 1 x Westinghouse 5u4 and some big transformers.
Would anyone be able to check out the pictures and let me know what you think?
It looks reasonable well put together to me, and is reported to sound great, but I wouldn't have a chance to hear it before buying.
Are there any obvious good points or dodgy / dangerous things to look out for?
Is it a popular kit/design or something more homebrew?
Thanks in advance,
James
I've been offered an amp, but the seller knows very little about it other than that it has 2 x el34, 1 x 6sl7 and 1 x Westinghouse 5u4 and some big transformers.
Would anyone be able to check out the pictures and let me know what you think?
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
It looks reasonable well put together to me, and is reported to sound great, but I wouldn't have a chance to hear it before buying.
Are there any obvious good points or dodgy / dangerous things to look out for?
Is it a popular kit/design or something more homebrew?
Thanks in advance,
James
Looks like your typical run-o-the-mill Single Ended amplifier.
Wiring could be neater so there MIGHT be some hum but the regular suspects like heater wires are twisted so at least the builder is aware of such issue.
The volume pot looks of good quality ALPS.
The output transformers are properly sized.
Do you have the speaker for them? Single Ended amp needs to be coupled to sensitive speakers.
If it were me, i would buy it.
Wiring could be neater so there MIGHT be some hum but the regular suspects like heater wires are twisted so at least the builder is aware of such issue.
The volume pot looks of good quality ALPS.
The output transformers are properly sized.
Do you have the speaker for them? Single Ended amp needs to be coupled to sensitive speakers.
If it were me, i would buy it.
Looks a lot like Hammond iron. I agree with JonSnell, if it's cheap, go for it. Hammond iron is usually quite good. But I also agree that the build is not the cleanest possible work, though not outright shoddy either. I've seen builds that make me only want to rip everything out of the chassis and build the thing again from scratch.
A schematic would help a lot...
A schematic would help a lot...
Thanks guys, really appreciate it.
I found out a bit more today.
Transformers are all Hammond classic with 1627 output transformers.
It's been originally built to the JE labs schematic.
I agree, it could do with a tidy up and moving components closer to where they're being used, but it'll sound nice and give me a good idea of whether I get on with a SET amp, so I'll give it a go.
I'm replacing a kel84 in triode mode running approx 5w into some heybrook sextets, so I'm good with the low power output.
Thanks again,
James
I found out a bit more today.
Transformers are all Hammond classic with 1627 output transformers.
It's been originally built to the JE labs schematic.
I agree, it could do with a tidy up and moving components closer to where they're being used, but it'll sound nice and give me a good idea of whether I get on with a SET amp, so I'll give it a go.
I'm replacing a kel84 in triode mode running approx 5w into some heybrook sextets, so I'm good with the low power output.
Thanks again,
James
One thing though. If the EL34's are run in triode, the 6SL7 is a little weak driver alone for them. I designed a basic EL34 single ended a couple of years ago with Hammond 125FSE's run at 5k primary. I used a 6SL7 input stage DC-coupled to a 6J5 cathode follower to achieve some kind of slew rate driving the EL34 grids. Does sound nice, though.
At least you'll get some quite decent OPT's for your money.
At least you'll get some quite decent OPT's for your money.
Cheap ampl. with cheap parts inside. Power in triod mode about 3 wt, if it enough for Your speakers. In penthode mode - about 6-7 wt, but with sharp sound from EL34, that will press You after one or two hour. IMO, I don't like EL34 in penthode mode with it "guitar" sound. I don't know what kind of OT, but they looks maybe good with big iron. All irons look good.
In Your place I will buy it and change EL34 to 6AS7, maybe in single or parallel mod , if OTs allow, acc. new schematic with really better sounding.
In Your place I will buy it and change EL34 to 6AS7, maybe in single or parallel mod , if OTs allow, acc. new schematic with really better sounding.
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why not audition it first then when its good sounding , buy it. Why bother to modify it.
Neat and tidy wiring, beautiful look, expensive parts doesn't mean a very nice sounding amp..
Look at ones in the net for sale...very good looking, good specs but some sound never mine...those needs a real modifications...
Neat and tidy wiring, beautiful look, expensive parts doesn't mean a very nice sounding amp..
Look at ones in the net for sale...very good looking, good specs but some sound never mine...those needs a real modifications...
Of course, different tubes, different schematic. IMO, twin triod 6AS7 sounds better penthod/triod mode EL34...I prefer 6AS7 RCA, GE. /Ri EL34 in triod is less 1 kom, Ri 6AS7 is about 500 ohm. If OT is 3-5 kohm it will be suitable....Ra OT is = 3-7 multiply to Ri. I would try with adjusting and PS, maybe second coil has middle point, maybe will sell PT and buy new... I have a schematic, I made the same 2 years ago.
I would buy this box....good enclosure, big irons, poti, sockets,....I will change all stuff inside to good resistors, caps - Rubycon, Elna, Nichikon. I don't like this condition on the photos.
I would buy this box....good enclosure, big irons, poti, sockets,....I will change all stuff inside to good resistors, caps - Rubycon, Elna, Nichikon. I don't like this condition on the photos.
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Thanks guys. I have bought it for the same cost as just buying the Hammond transformers. Soon I get to hear it 
Then it's a question of how long before I get the itch to change something... Usually not very long but we will see
Azazello, could you post the schematic for your 6as7 version please?
Thanks,
James
Then it's a question of how long before I get the itch to change something... Usually not very long but we will see
Azazello, could you post the schematic for your 6as7 version please?
Thanks,
James
A bit late, but my 2 cents..
If you have it, check for humming power transformer (mechanical) and check if it is not running hot (>55degrees Celsius)..
All other issues can be straightened out..
Listen to it first, for a longer period, before modding it.. EL34 wired both triode and pentode can sound just fine (imo).
Oh, and don't let the "cheap" parts mislead you.. Only using "expensive/audiophile" parts is not a guarantee that it will sound good. Matching (cheaper) parts is of bigger importance than just use expensive parts..
If you have it, check for humming power transformer (mechanical) and check if it is not running hot (>55degrees Celsius)..
All other issues can be straightened out..
Listen to it first, for a longer period, before modding it.. EL34 wired both triode and pentode can sound just fine (imo).
Oh, and don't let the "cheap" parts mislead you.. Only using "expensive/audiophile" parts is not a guarantee that it will sound good. Matching (cheaper) parts is of bigger importance than just use expensive parts..
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I kind of agree with azazello, but never forget that it doesn't matter how good your parts are in a bad design. In a good design they will might just bring it into something wonderful though.
Anyway - Hope the mains transformer is good. And you got a choke out of it and a couple of single ended transformers with decent iron. You should map out the schematic. Hope the power supply is choke input. Lots of room still in this Chassis for mods if you want to.
the OPT's have impedance of 2.5K -which is good for the EL34 plate resistance of around 900 ohms... but other choices exist so you can definitely mod. I might be tempted to try triode connected KT88 or 6550's
You could also parallel EL84' (6bq5)- which are pretty cheap and sound damn good - completely undervalued tube - they use smaller 9 pin sockets though. The chassis already has an extra hole in it behind the rectifier. These are just ideas.
IMHO - the humble 6AS7 might not be my first choice with this OPT - with a plate resistance of only 280 ohms per plate (140 Ohm in parallel) this OPT might present such a big load that you might not get much sound out of it..... Someone tell me if I am completely wrong here.
It probably sounds pretty good already. Have you hooked it up yet?
Anyway - Hope the mains transformer is good. And you got a choke out of it and a couple of single ended transformers with decent iron. You should map out the schematic. Hope the power supply is choke input. Lots of room still in this Chassis for mods if you want to.
the OPT's have impedance of 2.5K -which is good for the EL34 plate resistance of around 900 ohms... but other choices exist so you can definitely mod. I might be tempted to try triode connected KT88 or 6550's
You could also parallel EL84' (6bq5)- which are pretty cheap and sound damn good - completely undervalued tube - they use smaller 9 pin sockets though. The chassis already has an extra hole in it behind the rectifier. These are just ideas.
IMHO - the humble 6AS7 might not be my first choice with this OPT - with a plate resistance of only 280 ohms per plate (140 Ohm in parallel) this OPT might present such a big load that you might not get much sound out of it..... Someone tell me if I am completely wrong here.
It probably sounds pretty good already. Have you hooked it up yet?
Pick up a copy of "Valve Amplifiers" by Morgan Jones, either 3rd of 4th edition. He doesn't like single ended amps thou.
jeff
It could be decent for a 5 clean watts per channel amp. 10 watts of noise max (very distorted), but probably only around 5 watts with less than 1% distortion. I built a guitar amp with a 12AX7 driving a SE EL34. It sounds great for blues guitar, but I would never want so few clean watts for Hi-Fi. If your speakers are very efficient (95dB+), 5 watts may be enough to make you happy.
Pick up a copy of "Valve Amplifiers" by Morgan Jones, either 3rd of 4th edition. He doesn't like single ended amps thou.
jeff
Second that.
I personally find directly heated triodes a better choice for single ended. Fewer watts, but if your speakers are high sensitivity then it is wonderful.
You could do 2a3 (watch the 2.5 V filament voltages) or 6B4G (will likely need DC filaments).
It might sound a bit esoteric now, but you could run 6B4G in DC but close to ground (similar to what Thomas Mayer describes as filament bias), but use -50V grid bias with a morgan jones 'thingy' to reject noise...
The size of those OPT's mean that you will likely get very good bass response.
I have done this sort of thing since ages
Ian
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