My son wants a low output practice guitar amp. It needs superb clean tones and great crunch but no fancy high gain stuff as he has plenty of pedals for that stuff...
So what to build? Any suggestions?
My inital thoughts are to use two ECL80's witha EZ80 rectifier. The two triode stages should have enogh gain with a tone stack inbetween (propbably Steve Bench's design) and run the output stage push pull triode or pentode... The conventional design would be switchable but I've been toying with using a pot. to vary the triode to pentode percentage... Has anyone tried this or have a view on how it would work - or wouldn't work! see drawing below...
Any suggestions or thoughts would be most welcome.
ciao
James
So what to build? Any suggestions?
My inital thoughts are to use two ECL80's witha EZ80 rectifier. The two triode stages should have enogh gain with a tone stack inbetween (propbably Steve Bench's design) and run the output stage push pull triode or pentode... The conventional design would be switchable but I've been toying with using a pot. to vary the triode to pentode percentage... Has anyone tried this or have a view on how it would work - or wouldn't work! see drawing below...
Any suggestions or thoughts would be most welcome.
ciao
James
Attachments
Are you sure you want to use ECL80s? The gain of the triode section is quite low and even in pp operation I doubt they would give more than 3w and the anode load is quite high, although the power consumption would easy be handled by an EZ80. I can recall only ever seeing one circuit using ECL80s in pp for a gram amp.
Did you mean ECL82s or other triode/pentodes by any chance? I ask because the ECL80 has a common cathode, yet your schematic shows different cathodes for the triode and pentode.
Did you mean ECL82s or other triode/pentodes by any chance? I ask because the ECL80 has a common cathode, yet your schematic shows different cathodes for the triode and pentode.
I made the AX84 (www.ax84.com) using a 6X4 tube rectifier which was ok, but didn't have the "right" tone for me. The 4W or so that it creates is plenty of power though! I can't turn it up to distortion, its too loud for my room/the neighbours.
If you get a big guitar speaker, they can be 100dB efficient or more, which means that even 1W will be pretty loud. I have heard of people using a 12AU7 in PP as an output tube for 1W, apparently its quite good! (and distorts at usable volumes I would guess.)
BTW I am currently building a copy of a Fender Deluxe PP 6V6 for a friend (first paid project! 😀)
If you get a big guitar speaker, they can be 100dB efficient or more, which means that even 1W will be pretty loud. I have heard of people using a 12AU7 in PP as an output tube for 1W, apparently its quite good! (and distorts at usable volumes I would guess.)
BTW I am currently building a copy of a Fender Deluxe PP 6V6 for a friend (first paid project! 😀)
Hi Bournville,
I was thinking of using it fixed bias - with cathode grounded and the ECL80 is lower power than the 82... I am only looking for about 1Wish in triode mode and a bit more in pentode is OK... Do you think this would work?
Using the ECL82 is a definite possiblity (actually PCL82 as I can get them for 3euros)
For gain I would cascade the two triodes and use an IT for SE to PP... should be okay for clean - not sure for crunch yet (I guess I could add a pentode front end to take care of that...)
Most of the time on clean it will run at about 100mW or less into a 12" cab of 94dB/1W/1m sensistivity. It's a practice amp. My son has a 200W Hughes and Kettner system for gigging that is incredibly loud but a bit hard to tame in his bedroom 😉
thanks
Jmaes
I was thinking of using it fixed bias - with cathode grounded and the ECL80 is lower power than the 82... I am only looking for about 1Wish in triode mode and a bit more in pentode is OK... Do you think this would work?
Using the ECL82 is a definite possiblity (actually PCL82 as I can get them for 3euros)
For gain I would cascade the two triodes and use an IT for SE to PP... should be okay for clean - not sure for crunch yet (I guess I could add a pentode front end to take care of that...)
Most of the time on clean it will run at about 100mW or less into a 12" cab of 94dB/1W/1m sensistivity. It's a practice amp. My son has a 200W Hughes and Kettner system for gigging that is incredibly loud but a bit hard to tame in his bedroom 😉
thanks
Jmaes
Hi Shifty,
I've spent time on the AX84 site and thought of a moonlight... but I want to design my own take on it🙂
I had to try quite a few speakers before I could find a relatively low efficent one that had the right tone...
Congrats on the paid work! Long may it last!
ciao
Jmaes
I've spent time on the AX84 site and thought of a moonlight... but I want to design my own take on it🙂
I had to try quite a few speakers before I could find a relatively low efficent one that had the right tone...
Congrats on the paid work! Long may it last!
ciao
Jmaes
ECL80s
I admit that it is many years since I've used these tubes, but I remember I did have problems with stability because of the common cathode, because the bias arrangements for the triode and pentode sections are different.
I have not used a fixed bias arrangement with these tubes so cannot comment on it - I used cathode bias on the pentode and grid bias on the triode (via a large grid leak connected between grid and cathode - I think I used 10meg!) with a large bypass cap on the common cathode resistor to get rid of any tendency to instability - 250uf or so.
Other circuits I've seen use NFB between the anodes to keep the circuit stable, but this reduces the gain, and with ECL80s there really is not a lot to play with.
I don't think that ECL80s had much of a run as audio amps in addition to their other duties in old TVs because the ECL82 came out shortly after their introduction. The most innovative circuit using a ECL80 I've seen had it as a complete TRF receiver, using the pentode stage as an RF amp, the triode as a leaky-grid detector, and then the pentode stage reflexed back as an output stage! I must ask though, that since a single E/PCL82 would give just as much output as a pp ECL80 circuit, and this is a practice amp, not a hifi one, why not use it?
I admit that it is many years since I've used these tubes, but I remember I did have problems with stability because of the common cathode, because the bias arrangements for the triode and pentode sections are different.
I have not used a fixed bias arrangement with these tubes so cannot comment on it - I used cathode bias on the pentode and grid bias on the triode (via a large grid leak connected between grid and cathode - I think I used 10meg!) with a large bypass cap on the common cathode resistor to get rid of any tendency to instability - 250uf or so.
Other circuits I've seen use NFB between the anodes to keep the circuit stable, but this reduces the gain, and with ECL80s there really is not a lot to play with.
I don't think that ECL80s had much of a run as audio amps in addition to their other duties in old TVs because the ECL82 came out shortly after their introduction. The most innovative circuit using a ECL80 I've seen had it as a complete TRF receiver, using the pentode stage as an RF amp, the triode as a leaky-grid detector, and then the pentode stage reflexed back as an output stage! I must ask though, that since a single E/PCL82 would give just as much output as a pp ECL80 circuit, and this is a practice amp, not a hifi one, why not use it?
Bournville said
Good question! I guess partially because I've using ECL82s so the ECL80 would be different! Partially because it gives lower power pp and if it's works I'll build myself one for my bass (so pp is better than se...).
I'm not wedded to the 80s so the 82 SE is a real possibility. I guess the OPT will cost more for the SE so that might tip the balance...
Thanks for your recollections on the 80 - fascinating stuff - particularly the TRF reciever - that's really nice!
ciao
James
Good question! I guess partially because I've using ECL82s so the ECL80 would be different! Partially because it gives lower power pp and if it's works I'll build myself one for my bass (so pp is better than se...).
I'm not wedded to the 80s so the 82 SE is a real possibility. I guess the OPT will cost more for the SE so that might tip the balance...
Thanks for your recollections on the 80 - fascinating stuff - particularly the TRF reciever - that's really nice!
ciao
James
Just in case its any help, a great source of parts for this kind of thing is old tube reel to reel recorders... There are lots around in junk stores, no-one wants em!
You will get sockets, transformers, tubes, power cable and lots of stuff, sometimes even a funky tweed case!
Just a thought.
You will get sockets, transformers, tubes, power cable and lots of stuff, sometimes even a funky tweed case!
Just a thought.
... Take the good advice...
Hi Bournville,
Having spent my lunch break running some calculations - I can see that you are completely correct about the low gain and high Zout of the ECL80. It would be diffcult to make a good guitar amp from them...
So back to good old P/ECL82s. Plenty of gain in the triode sctions to drive a tone stack and get some 'crunch'.
I can run a relatively high Z OPT to reduce the output power and ensure that I can crash the psu rails for extra crunch too...
Thanks for the advice - sometimes I do listen
ciao
James
Hi Bournville,
Having spent my lunch break running some calculations - I can see that you are completely correct about the low gain and high Zout of the ECL80. It would be diffcult to make a good guitar amp from them...
So back to good old P/ECL82s. Plenty of gain in the triode sctions to drive a tone stack and get some 'crunch'.
I can run a relatively high Z OPT to reduce the output power and ensure that I can crash the psu rails for extra crunch too...
Thanks for the advice - sometimes I do listen
ciao
James
Princeton Mod
James,
The best low-wattage guitar amp I've ever played is my version of a tweed Fender Princeton that I built. One 6V6 single-ended into a Hammond 125ESE, about 4.5 watts. It's very clean up to about 3/4 of the volume control, then it has a smooth, old fashioned break up. Very good note definition too.
A similar "project" is posted on the Angela Instruments website. But, I would suggest adding a 15 Henry choke after the rectifier, like I did. I also used a 6SL7 instead of a 12AX7. It's a lot more clean and defined than a stock Princeton, but if you want it to be dirtier you can use a smaller output transformer.
Other modifications from the original circuit include taking out the horrible tone control network and replacing it with an old Gibson style one - two coupling caps, a 0.1uF and a 750pF, with a 1 meg pot to switch between the two. Works great.
I hate the marshall/fender "tone stack" too. It can't boost the mids at all, and has very little usable range due to the steep slope.
Joel
James,
The best low-wattage guitar amp I've ever played is my version of a tweed Fender Princeton that I built. One 6V6 single-ended into a Hammond 125ESE, about 4.5 watts. It's very clean up to about 3/4 of the volume control, then it has a smooth, old fashioned break up. Very good note definition too.
A similar "project" is posted on the Angela Instruments website. But, I would suggest adding a 15 Henry choke after the rectifier, like I did. I also used a 6SL7 instead of a 12AX7. It's a lot more clean and defined than a stock Princeton, but if you want it to be dirtier you can use a smaller output transformer.
Other modifications from the original circuit include taking out the horrible tone control network and replacing it with an old Gibson style one - two coupling caps, a 0.1uF and a 750pF, with a 1 meg pot to switch between the two. Works great.
I hate the marshall/fender "tone stack" too. It can't boost the mids at all, and has very little usable range due to the steep slope.
Joel
Joel,
Thanks for your reply... a baby Princeton is an interesting idea. I'll check the reference...
Changing the 12Ax7 sounds like a good idea...and chyanging the tone stack is a must! The Fender or Marshall tone stacks are horrible! Your suggestion of the Gibson is an interesting idea. I've never used a Gibson amp so I'll try your suggestion out.
Thanks
Jmaes
Thanks for your reply... a baby Princeton is an interesting idea. I'll check the reference...
Changing the 12Ax7 sounds like a good idea...and chyanging the tone stack is a must! The Fender or Marshall tone stacks are horrible! Your suggestion of the Gibson is an interesting idea. I've never used a Gibson amp so I'll try your suggestion out.
Thanks
Jmaes
James,
Yes, I remember once trying to sort out an output tranny for the ECL80 - they were sold under the description of "suitable for a small output pentode" and were the same as used in battery tube sets - the primary impedence was about 10-11k!
The P/ECL82 seems a much easier option. Good luck on the project.
In the UK I occasionally pick up old recorders at 'car boot' sales - usually about £5 ($8) a time, and they often contain a range of useful audio valves in good condition - ECL82s, EL84s, EF86s and ECC83s being the most common found, and Mullard the most common brand.
Yes, I remember once trying to sort out an output tranny for the ECL80 - they were sold under the description of "suitable for a small output pentode" and were the same as used in battery tube sets - the primary impedence was about 10-11k!
The P/ECL82 seems a much easier option. Good luck on the project.
ShiFtY said:
In the UK I occasionally pick up old recorders at 'car boot' sales - usually about £5 ($8) a time, and they often contain a range of useful audio valves in good condition - ECL82s, EL84s, EF86s and ECC83s being the most common found, and Mullard the most common brand.
I made a VERY small practice amp a while ago as a gift for my brother in law. I used a single ECC81 (12AT7) using one half as preamp and the other as "power" amp. The output trannie was from an old radio and had a 7k/4 ohm ratio. The speaker was a 4" 16 ohm fullrange unit.
Unfortunately the gain was a bit low so I had to add a SS diode clipper to get some decent heavy metal distortion.
Maybe not the best guitar amp ever, but fun as hell to build, especially as it didn´t cost me a thing!
Unfortunately the gain was a bit low so I had to add a SS diode clipper to get some decent heavy metal distortion.
Maybe not the best guitar amp ever, but fun as hell to build, especially as it didn´t cost me a thing!
Neat!
I did a similar thing with EF86 into ECC82, a pair of 1N914s and a 6" by 4" ellipitical speaker... it was great fun but didn't really challange a proper guitar amp! I did try it into a cab but it really wasn't good enough...
ciao
James
I did a similar thing with EF86 into ECC82, a pair of 1N914s and a 6" by 4" ellipitical speaker... it was great fun but didn't really challange a proper guitar amp! I did try it into a cab but it really wasn't good enough...
ciao
James
...I remember some weeks ago reading an article in an old radio mag which made great claims for the PCC88 rf double triode in small pp output stages. Originally designed for work in TV tuners, in pp mode, with fixed bias of -6v and a 200v on the anodes, output of 1.5w can be obtained, and at its maximum ratings, with fixed bias of -5v and 210v on the anodes, output goes up to 2.5w. The output tranny had a 10k anode to anode impedence. It could thus rival a SE P/ECL82 amp which is typically used in circuits giving 2.5w out, and is certainly more powerful than an ECC82 used in pp.
The heater is more of a problem though, being 7.6v...
The heater is more of a problem though, being 7.6v...
... PCC88...
Now that is tempting! And one could overdrive the power stage nicely too...
Does anyone have a view on triode mode versus pentode mode for a guitar amp?
How about DHT (31?) for a guitar amp?
Now that is tempting! And one could overdrive the power stage nicely too...
Does anyone have a view on triode mode versus pentode mode for a guitar amp?
How about DHT (31?) for a guitar amp?
Re: ... PCC88...
Not recommended. They are too microphonic, IMO.
And, I have to think that any benefit of using a DHT would be fruitless with such a low bandwidth source as a guitar.
I have wanted to do an all triode guitar amp though! Yum. Probably the best bet is something like PP 6L6's in triode mode. 3 watts or so at 2% distortion.
James D. said:
Not recommended. They are too microphonic, IMO.
And, I have to think that any benefit of using a DHT would be fruitless with such a low bandwidth source as a guitar.
I have wanted to do an all triode guitar amp though! Yum. Probably the best bet is something like PP 6L6's in triode mode. 3 watts or so at 2% distortion.
DHTs
Good point! So no DHT combo 🙁
I'll forgive you for liking 6L6's - the EL84 is better 🙂
Actually I like both in guitar amps a lot.
There is something nice about all triodes for good clean tones - but don't you think pentodes are nice for overdriven rock tones?
Good point! So no DHT combo 🙁
I'll forgive you for liking 6L6's - the EL84 is better 🙂
Actually I like both in guitar amps a lot.
There is something nice about all triodes for good clean tones - but don't you think pentodes are nice for overdriven rock tones?
James D. said:
As I said, my favorite guitar amp uses a single 6V6 in pentode mode. I don't use many overdriven rock tones, but for clean jazz and country stuff it's the best.
I think people who want crazy overdriven distortion at bedroom volume levels need to really consider amps with a Master Volume control. Otherwise you need to limit yourself to an amp that hits the wall at milliwatts of output.
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