Hey!
So, it's been a while, I know. Things got a bit sticky here at the Annan household over the last year or so and I was not able to keep a presence at DIYAudio for some time. Everything is coolsville now though, so it's time for another project.
This time, I'm looking to build a push-pull amp for a friend. He's currently got a small set of Polk Audio bookshelf speakers (meh) and a 12 x 16 room so I'm thinking a modest push-pull amp would do the trick.
I'll need to come in under $500 for the project and I would like it to push about 15 - 20 watts, but more would be great. Here are the designs I'm considering:
1. The new Pete Millett Engineer's Amplifier (I love Pete's stuff and I always wanted to one of his designs)
2. SY's Red Light District
3. Gingertube's Baby Huey
4. Another Morgan Jones Bevois Valley
5. Some other monster KT88 PP or somesuch
Any recommendations among these listed or others I should consider?
Thanks in advance for any advice you can give. Dumb Kofi questions to follow...
Just like old times.
Kofi
So, it's been a while, I know. Things got a bit sticky here at the Annan household over the last year or so and I was not able to keep a presence at DIYAudio for some time. Everything is coolsville now though, so it's time for another project.
This time, I'm looking to build a push-pull amp for a friend. He's currently got a small set of Polk Audio bookshelf speakers (meh) and a 12 x 16 room so I'm thinking a modest push-pull amp would do the trick.
I'll need to come in under $500 for the project and I would like it to push about 15 - 20 watts, but more would be great. Here are the designs I'm considering:
1. The new Pete Millett Engineer's Amplifier (I love Pete's stuff and I always wanted to one of his designs)
2. SY's Red Light District
3. Gingertube's Baby Huey
4. Another Morgan Jones Bevois Valley
5. Some other monster KT88 PP or somesuch
Any recommendations among these listed or others I should consider?
Thanks in advance for any advice you can give. Dumb Kofi questions to follow...
Just like old times.
Kofi
Hi Kofi! The UN isn't the same without you.
Your biggest cost item is probably going to be the OP transformers but you might find some good bargains on eBay. Stick to economical tubes that suit the OPTs you select (i.e. avoid DHTs, KT88s and other costly bottles).
Your biggest cost item is probably going to be the OP transformers but you might find some good bargains on eBay. Stick to economical tubes that suit the OPTs you select (i.e. avoid DHTs, KT88s and other costly bottles).
If you are building it for a friend, you might want to stick with something that uses tubes that they will not have trouble sourcing in the future. That's my only "thing" with Pete's amp. Otherwise it is awesome and has a lot of potential to go further. 🙂
What about:
4.5) Some other medium-sized EL34 PP or somesuch
🙂
What about:
4.5) Some other medium-sized EL34 PP or somesuch
🙂
Initially, I was worried about the "future" tube availability issue as well.
So before I built Pete's amp, I checked my sources for the required tubes.
I now have more than a "lifetime" supply.
Also, the design is conservatively rated. The tubes are not working hard, so should last a long time.
I'm very happy with the Millett "Engineer's Amplifier". It's the best tube project I have ever built. Highly recommended by this hobbyist.
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You may want to consider this one. The Simple EL84: auto inverting with CCS. It is super simple which leaves you a lot of money for good OPTs
Updating the Simple EL84
Updating the Simple EL84
You could add George from Tubelab's new Simple PP board to the list too. Great support as I've seen. He has new section now in diyaudio under Vendor Forms.
#1. If you need more power still at low cost/ but great sound.
Under the thread on Pete's amp it has been mentioned that it could be converted to use present production tubes. Maybe one could look at that. I don't think it's too much of a problem to even run wires to sockets like ST-70 amps do. As George (Tubelab) says values of caps would have to be changed to a higher Voltage as he did with bigger sweep tubes when he increased power. He also mentions lifting resistors to change screen voltage supply along with some rewiring to board.
Plate voltage may be okay for a number of lower cost OT tubes 6L6GC 6CA7 & EL 34. I've seen there are new production 807 tubes out there for low cost. Maybe they could be run a bit harder? EH6CA7 @ $80 look like a great value and sound for $. KT-88's could be added later with bigger PS Trans or could be run at lower points for longer life.
Using Edcor OT as Pete used, but uprated to 100W rating say 4.2K Primary @ about $93 ea. Bigger PS Trans. shouldn't cost much more if needed.
OT tubes $60-80. Might be able to make it work for $500 or a bit more plus have more reserve power with at least 30W/CH depending on which tubes and how they are run. Cabinet or chassis would be extra.
If that's too much money maybe 6V6GT or EL84 @ $40-60 would work saving tube and OT trans. cost. A 8-10K Primary OT would be needed so existing one in BOM would work. 10K would be better for 6V6GT. Should get 12-18W depending how hard tubes are pushed. 6V6GT's worth a watt or two less per CH. PS changes again need to. Maybe simpler and less costly.
I've read Genelex New production EL84 & Tungsol 6V6GT's are amongst the best sounding today. Equal or close to NOS.
Russian NOS OT's could be run for all of the above for less $ though I read 6V6 types aren't very tough or good sounding. 6N3C-E for 6L6 types are liked too.
I don't know what present production tubes would work for input?
Seems like a great design with distortion cancellation loops like Cit II, so should sound great. Maybe this would be enhanced with regular audio tubes!
As Pete mentioned you could also use higher end OT for less distortion and increased frequency response range.
I have this board so would like set it up for production tubes too!
What mods are needed?
Cheers!
Randy
#1. If you need more power still at low cost/ but great sound.
Under the thread on Pete's amp it has been mentioned that it could be converted to use present production tubes. Maybe one could look at that. I don't think it's too much of a problem to even run wires to sockets like ST-70 amps do. As George (Tubelab) says values of caps would have to be changed to a higher Voltage as he did with bigger sweep tubes when he increased power. He also mentions lifting resistors to change screen voltage supply along with some rewiring to board.
Plate voltage may be okay for a number of lower cost OT tubes 6L6GC 6CA7 & EL 34. I've seen there are new production 807 tubes out there for low cost. Maybe they could be run a bit harder? EH6CA7 @ $80 look like a great value and sound for $. KT-88's could be added later with bigger PS Trans or could be run at lower points for longer life.
Using Edcor OT as Pete used, but uprated to 100W rating say 4.2K Primary @ about $93 ea. Bigger PS Trans. shouldn't cost much more if needed.
OT tubes $60-80. Might be able to make it work for $500 or a bit more plus have more reserve power with at least 30W/CH depending on which tubes and how they are run. Cabinet or chassis would be extra.
If that's too much money maybe 6V6GT or EL84 @ $40-60 would work saving tube and OT trans. cost. A 8-10K Primary OT would be needed so existing one in BOM would work. 10K would be better for 6V6GT. Should get 12-18W depending how hard tubes are pushed. 6V6GT's worth a watt or two less per CH. PS changes again need to. Maybe simpler and less costly.
I've read Genelex New production EL84 & Tungsol 6V6GT's are amongst the best sounding today. Equal or close to NOS.
Russian NOS OT's could be run for all of the above for less $ though I read 6V6 types aren't very tough or good sounding. 6N3C-E for 6L6 types are liked too.
I don't know what present production tubes would work for input?
Seems like a great design with distortion cancellation loops like Cit II, so should sound great. Maybe this would be enhanced with regular audio tubes!
As Pete mentioned you could also use higher end OT for less distortion and increased frequency response range.
I have this board so would like set it up for production tubes too!
What mods are needed?
Cheers!
Randy
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Ran out of time to make corrections.
I should say Pete first mentioned increasing PS Voltage is possible if Cap value is increased in voltage appropriately.
EH6CA7 should be EH 6CA7.
5881, 7591, 7868, KT-66, & KT-77 also in new production should work too.
Maybe NEW Tung Sol KT-120 coming in May would work too!
Randy
I should say Pete first mentioned increasing PS Voltage is possible if Cap value is increased in voltage appropriately.
EH6CA7 should be EH 6CA7.
5881, 7591, 7868, KT-66, & KT-77 also in new production should work too.
Maybe NEW Tung Sol KT-120 coming in May would work too!
Randy
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Noted! Although I think I may go with the Bevois Valley amp before this EL34 amp one as I've made one before and it was very will received.
I know... but the non-economical ones are WHEEEEEEEE!!!!
Yeah-- but I might see if it can stretch...
Perhaps... what does the EL34 have that is different than the EL84?
Hmmm... this is looking good to me. I agree that the tubes may be a problem to source at some point, but at that point he'll be asking for another amp, so....
Can't help you with the mods needed to convert the Millett boards to standard production tubes, but I'm not surprised one bit that it was George's suggestion to crank up the B+.
So, I'm going to run some numbers on the cost between the Bevois Valley, the Engineer's Amp and the Simple and / or El Cheapo and see where I can get some trade-offs. That will take a bit but will be worth the effort as I can present this to friend and he can help decide.
I may, however, chip in some cash myself and get him on some KT88s. Anyone got a good design for a bang-up push pull using a quad of these?
Thanks so much for all the responses. I've forgotten what a great forum this is and what special people I've "met".
"Kofi"
re: New production tubes on Big Red Engineer's Amplifier Board.
KT-88 would be another popular one. Call it red hot rocket then! Just wait for KT-120, though would be pretty expensive @ $70+ each. Might be worth it if lasts for years if run at low a point as possible for long life. Still would have plenty of power.
Pete or George whom have the most experience with it will probably come up with an answer when they have time!
Randy
KT-88 would be another popular one. Call it red hot rocket then! Just wait for KT-120, though would be pretty expensive @ $70+ each. Might be worth it if lasts for years if run at low a point as possible for long life. Still would have plenty of power.
Pete or George whom have the most experience with it will probably come up with an answer when they have time!
Randy
I have used my red board for a whole bunch of experiments, with more to come in the future. For now it is a source of amusement and education. I have no plans to make a complete amplifier out of it any time soon, if at all.
I have run at least a dozen different output tubes through it with power outputs from 25 WPC to 200 WPC. There are so many different tubes that work in this board without modification (cheap ones too), why use expensive new production tubes.
I haven't tried any of them, but the typical audio tubes require a lot more screen voltage than the typical sweep tube. Petes board runs the screens of the input tube and the output tube from the same 150 volt supply. A KT88 would need 300+ volts on the screen which is too much for a 6CB6 so an additional regulator is needed.
I know from asking a similar question that Eli recommends his "El Cheapo" but using 7591 output tubes, ""El Cheapo Grande". Apparently 7591 has modest drive requirements (similar to EL84), but much greater output power.
Maybe some of the audio tubes could be used with the g2 at plate voltage. For example, I think you can run the 6L6GC conservatively at 350V plate and g2 into 5K Zpre plate-plate and get about 30 W.
Michael
Kofi
Don't know what speakers you intend to hang behind that but perhaps you may consider another approach: a SE amp and some sensitive speakers. reason why I say this is that push-pull amps by definition have cancellation of the 2nd order harmonic but not of the odd harmonics. The 2nd is not considered to be extreemly harmfull.
The RH807 from Alex Kitic comes to mind and Kegger also has some very fine design on the other website.
If sticking with a push pull then by all means go for the 6L6GC which was designed specificially for push pull operation and has a very high amount of 2nd order but a low 3rd order distortion (2nd order being cancelled). These tubes are plentyfull and relatively cheap. If you do like this then you may want to try the amp in triode mode and then you can also put in the Kt-66 (like the famed Quad II amp).
Hope this helps
AM
I just bought a dozen Chinese 6L6GCs for $3 each. That's $1 less than the sweep tubes I bought for the red board. 😉
This is a common arangement. Over a million guitar amps can't all be wrong. Cheap Chinese 6L6GC can work at plate = screen up to about 450 volts.
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