Inspiration for amp project wanted
- Thread starter Tubetec
- Start date
Help Support GroupDIY Audio Forum:
Hi PRR,
Yes indeed your right ,450ma for the 6v6 vs 750ma for the EL84,its something I had noted previously ,but I reverted to the assumption that the EL84 being the more modern style tube was less power hungry in terms of the heaters .
Roughly the same in terms of HT requirements,max dissipation and load impedence ,a bit more drive voltage required by the 6V6 under similar conditions .
For rock and roll guitar I think either tube will work ok in this build ,but thanks for pointing out the difference all the same.
Do you have any particular favourites in the 15-20 watt class of amplifier yourself or interesting tone controls setups?
Yes indeed your right ,450ma for the 6v6 vs 750ma for the EL84,its something I had noted previously ,but I reverted to the assumption that the EL84 being the more modern style tube was less power hungry in terms of the heaters .
Roughly the same in terms of HT requirements,max dissipation and load impedence ,a bit more drive voltage required by the 6V6 under similar conditions .
For rock and roll guitar I think either tube will work ok in this build ,but thanks for pointing out the difference all the same.
Do you have any particular favourites in the 15-20 watt class of amplifier yourself or interesting tone controls setups?
Diabolical Artificer
Active member
- Joined
- Aug 12, 2014
- Messages
- 32
Most EL84 guitar amps push the EL84 to it's limits with the result they go all brown. The 6V6 is in a bigger envelope so gets less hot.
As has been said start at the OP stage, but first what is your OPT's z ratio? This dictates what valves you can use etc. Also what are the mains tfmr specs? If it's beefy around 200mA with plenty of heater power you could use 807's or less common valves like the 6DQ6B or 6146's triode strapped, maybe Class A PP. You need to sit down and draw some load lines. Designing an amp from scratch rather than building from an existing design is more fun and you can make it completely custom.
Your OPT being UL would be best used to make a hifi type amp with NFB to get a clean, low distortion OP. you can always use a pedal to get distortion. A good clean amp is invaluable in a studio, great for vocals, acoustic, bass etc etc.
Lastly if you want to get interesting once the OP stage is sorted you could try a cascode LTP with active tone section, bootstrapped cathode follower drives et al.
Andy.
As has been said start at the OP stage, but first what is your OPT's z ratio? This dictates what valves you can use etc. Also what are the mains tfmr specs? If it's beefy around 200mA with plenty of heater power you could use 807's or less common valves like the 6DQ6B or 6146's triode strapped, maybe Class A PP. You need to sit down and draw some load lines. Designing an amp from scratch rather than building from an existing design is more fun and you can make it completely custom.
Your OPT being UL would be best used to make a hifi type amp with NFB to get a clean, low distortion OP. you can always use a pedal to get distortion. A good clean amp is invaluable in a studio, great for vocals, acoustic, bass etc etc.
Lastly if you want to get interesting once the OP stage is sorted you could try a cascode LTP with active tone section, bootstrapped cathode follower drives et al.
Andy.
Hi Dr Wobble,
Ive no real data on either of the transformers ,sizewise the mains tx isnt far off what you might find in many 50w amps ,maybe a little smaller than what you'd find in a vintage JMP 50. There's a couple of primary taps(220,230,240) ,centre tapped HT , heater and interwinding screen. Output certainly used EL84's a pair of em ,and again its a generously sized component . Going with a more hi-fi type setup sounds like a good plan ,would make a more versatile unit in the end as you pointed out .
When you say LTP with active tone , do you mean feedback to one grid of the LTP with tone switching ?
Id probably tend to stick with the more common type tubes, Ive had great success with sovtek hardened EL84/7198 variant ,but I also have a very nice set of Groove tubes 6V6's as well .
Ive no real data on either of the transformers ,sizewise the mains tx isnt far off what you might find in many 50w amps ,maybe a little smaller than what you'd find in a vintage JMP 50. There's a couple of primary taps(220,230,240) ,centre tapped HT , heater and interwinding screen. Output certainly used EL84's a pair of em ,and again its a generously sized component . Going with a more hi-fi type setup sounds like a good plan ,would make a more versatile unit in the end as you pointed out .
When you say LTP with active tone , do you mean feedback to one grid of the LTP with tone switching ?
Id probably tend to stick with the more common type tubes, Ive had great success with sovtek hardened EL84/7198 variant ,but I also have a very nice set of Groove tubes 6V6's as well .
here is my project for the moment.
Stereo amp , Main , Leslie amp 6973 output tubes. trying to incorporate all my ideas before doing any rework with the amp section.
So far I love playing the guitar straight into the Leslie amp side into the leslie speaker (10" jensen 1965 or so)
Stereo amp , Main , Leslie amp 6973 output tubes. trying to incorporate all my ideas before doing any rework with the amp section.
So far I love playing the guitar straight into the Leslie amp side into the leslie speaker (10" jensen 1965 or so)
Attachments
I used a leslie 122 on a few recording sessions ,for guitars mainly but underwater vocal sounds too.
The 122 amp requires a speaker level connection from the Hammond ,but the C-3 has an aux input around the back which works well with a buffered guitar signal ,a bit of fuzz added works nicely also .
I missed the chance of getting a hammond tone wheel organ for free sometime back ,was one of the last proper tone wheel units they made with all transistor electronics ,shame I missed it .
The 122 amp requires a speaker level connection from the Hammond ,but the C-3 has an aux input around the back which works well with a buffered guitar signal ,a bit of fuzz added works nicely also .
I missed the chance of getting a hammond tone wheel organ for free sometime back ,was one of the last proper tone wheel units they made with all transistor electronics ,shame I missed it .
Here's Mat Mahtias's Orange amp schematic,
note the F.A.C. bass switch (frequency attenuation capacitors) ,I might give it a try with a lorlin 12 way on this build .
PJ Baxandall had a similar thing on one of his preamps way back as well ,makes an excellent bass roll off for ribbon mikes. I'll post the schem of that from the original WW publication later .
note the F.A.C. bass switch (frequency attenuation capacitors) ,I might give it a try with a lorlin 12 way on this build .
PJ Baxandall had a similar thing on one of his preamps way back as well ,makes an excellent bass roll off for ribbon mikes. I'll post the schem of that from the original WW publication later .
Attachments
PRR,
I also note the use of the concertina phase splitter directly to the 100 watt output stage ,not such a common thing to see ,but in this case it does give a big clean tone ,more like a Hiwatt than most other Brit amps of the time .The transformers were huge in these things too . I guess what you gain in drive terms with the usual LTP set up is offset by the lower input impedence ,where the concertina doesnt load the preamp output nearly as much .
I also note the use of the concertina phase splitter directly to the 100 watt output stage ,not such a common thing to see ,but in this case it does give a big clean tone ,more like a Hiwatt than most other Brit amps of the time .The transformers were huge in these things too . I guess what you gain in drive terms with the usual LTP set up is offset by the lower input impedence ,where the concertina doesnt load the preamp output nearly as much .
I have to say I always found the original Orange graphic series an impressive feat of engineering, two preamp tubes ,and quad EL34 on output duties .
'The moment we become complacent enough to think we know it all is the moment wise words are wasted on us '
'The moment we become complacent enough to think we know it all is the moment wise words are wasted on us '
I’v e never thought about orange. You look at Brit amps an assume you know how they’re put together with a LTP. But a Concertina driver in that amp . Simple With only 2 12ax7’s and very loud with 4 EL 34s.
It is interesting. I did notice the coupling cap switch eq. I believe matchless used that later but orange was the first time I saw that used.
The EL84 makes me think of the circuit from Ken Fischer's Rocket. I have rolled a few of those for myself based on the schematics at the amp garage forum. It has a 4xEL84 output stage, but you could consider a two bottle version, adjusted for example with individual cathode bias.
It is a very touch sensitive amp, frighteningly honest. It really made me get my chops together. It is incredible with a Celestion Gold.
This circuit is more forgiving than the other TW circuits and you can go your own way with the layout. People have made them with 6V6, KT66 and KT77 too. The circuit is basically the bare bones of an AC30 without the bells and whistles. Like a cut-down Vespa.
It is a very touch sensitive amp, frighteningly honest. It really made me get my chops together. It is incredible with a Celestion Gold.
This circuit is more forgiving than the other TW circuits and you can go your own way with the layout. People have made them with 6V6, KT66 and KT77 too. The circuit is basically the bare bones of an AC30 without the bells and whistles. Like a cut-down Vespa.
andyfromdenver
Well-known member
what do you need/like? verb and term (It's hard for me to do without)? 1/2 channel?
Just to throw out what I love dearly, a top boost straight up vox with maybe minor changes to the el84 screens is a very cool amp.
I can show you a way on a pull switch to go from top boost tone stack to fender treb bass, but with just the top boost you can dial in some really awesome tones.
It would be good to know what the B+ under load will be for that PT. may need ss rect. tube rect. drop some Voltage.
I think it would be wise to build to what the PT and OT want versus forcing a circuit to accommodate.
I love a deluxe reverb and princeton reverb though.
My 15-20W range gigging amp is a Princeton Reverb with a Mercury Mag low B+ PT which let me go solid state rect and increased filtering. The OT is Deluxe reverb sized. B+ is about 410vdc and the amp is big and clean. I love it. Works great for rhodes too.
Just to throw out what I love dearly, a top boost straight up vox with maybe minor changes to the el84 screens is a very cool amp.
I can show you a way on a pull switch to go from top boost tone stack to fender treb bass, but with just the top boost you can dial in some really awesome tones.
It would be good to know what the B+ under load will be for that PT. may need ss rect. tube rect. drop some Voltage.
I think it would be wise to build to what the PT and OT want versus forcing a circuit to accommodate.
I love a deluxe reverb and princeton reverb though.
My 15-20W range gigging amp is a Princeton Reverb with a Mercury Mag low B+ PT which let me go solid state rect and increased filtering. The OT is Deluxe reverb sized. B+ is about 410vdc and the amp is big and clean. I love it. Works great for rhodes too.
Lots of stories about this being KF’s fav amp and pedal friendly. I have a 64 AC 30 that I added the top boost circuit to and it is a weird but effects EQ with large tonal ranges. Copied by vox from a Gibson amp. Consider to be a bad design that lived on. Also loved my old Princeton reverb. I was a fool to part with that thing.
So many amps and so little time.
Hi Andy, Tony and Fazer,
At this stage Im thinking 6V6's on main output duties ,then an EL84 based reverb driver ,that could also double up as another speaker output or even DI output . I'll go with the switched coupling cap for bass tweekage, I might fool around with duncans TSC to find some kind of mid suck,treble boost type scheme. I have the mains transformer mounted up on another chassis from a previous project that I changed my approach on later ,silicon rectifier and smoothing caps are in place so I'll be able to get an idea of what Ht volts might be soon .
At this stage Im thinking 6V6's on main output duties ,then an EL84 based reverb driver ,that could also double up as another speaker output or even DI output . I'll go with the switched coupling cap for bass tweekage, I might fool around with duncans TSC to find some kind of mid suck,treble boost type scheme. I have the mains transformer mounted up on another chassis from a previous project that I changed my approach on later ,silicon rectifier and smoothing caps are in place so I'll be able to get an idea of what Ht volts might be soon .
Nothing wrong with 6V6 for a guitar amp.
Understanding what options this iron gives you is certainly the first move.
I forgot to mention that the Fischer circuits all used relatively low B+. Mostly 260V off the PT. I doubt your iron will be that low.
Understanding what options this iron gives you is certainly the first move.
I forgot to mention that the Fischer circuits all used relatively low B+. Mostly 260V off the PT. I doubt your iron will be that low.
Unfortunately no tube rectifier heater winding on this mains transformer ,so SS rectifiers ,gives a bit of extra bite and attack to the sound in any case. From memory I think I was getting something like 350-370 volts dc off the rectifier with this transformer and that was with only a nominal current draw ,seems like a reasonable voltage for a PP 6V6 class A/B stage . I might need to RC drop the volts a bit for the single ended EL84 ,about 220volts dc is about right and ensures long tube life ,in any case the extra smoothing on the line will be a bonus as PSRR in a single ended stage in nowhere near what you get from PP. The cab is just shy size wise to house a long tank reverb which is a bit of a bummer,but I do have another larger Marshall cab housing a 12 inch speaker so that might well be a better starting point .
Bit of a cleanup opperation in progress here after the snow and ice ,my driveway was completely cut off by branches which came down under the weight of ice and snow , it was sheer luck the electricity wires werent damaged .The thaw is well underway here now ,so flooding is expected in certain areas.
Bit of a cleanup opperation in progress here after the snow and ice ,my driveway was completely cut off by branches which came down under the weight of ice and snow , it was sheer luck the electricity wires werent damaged .The thaw is well underway here now ,so flooding is expected in certain areas.
Tubetech, have you done the zener drop on the PT center tap? And or voltage scaling with a mosfet? These ways to adjust b+ are slick but could also be seen as weak links for on the road stability .
Never mind your el84 is your reverb driver. So RC string is the way to go.
Never mind your el84 is your reverb driver. So RC string is the way to go.
Hi Fazer,
I cant say Ive ever used Mosfet based regulators, its certainly a cost effective way to do things though .
I most likely will use LC and RC to supply the screens of my output tubes and onto the pre voltage stages .
I have a little project on the shelf I started a good while back employing PCL82's and a long chain of 5 volt Zeners for voltage reference (ala Morgan Jones) , more suitable for preamps than power output stages really ,I made two discrete tube regulators ,back to back ,mirror image from some tag strip, stand offs and tube sockets, I'll post a pic of that soon also .
I cant say Ive ever used Mosfet based regulators, its certainly a cost effective way to do things though .
I most likely will use LC and RC to supply the screens of my output tubes and onto the pre voltage stages .
I have a little project on the shelf I started a good while back employing PCL82's and a long chain of 5 volt Zeners for voltage reference (ala Morgan Jones) , more suitable for preamps than power output stages really ,I made two discrete tube regulators ,back to back ,mirror image from some tag strip, stand offs and tube sockets, I'll post a pic of that soon also .
For those with fairly high B+ available, but who still must have 6v6 in pp .... like me ... I can recommend the JJ 6V6S ... very nice sound and cost effective too.
Can happily live with B+ well beyond those typically found with typical 6v6gt - just the ticket for a ss rectifier (which has a much lower voltage drop than a rectifier tube).
Packs quite a wallop of watts for such low heater power. Great for 10Wrms of clean-ish power, up to 15W for 'crunch-ier'
Can happily live with B+ well beyond those typically found with typical 6v6gt - just the ticket for a ss rectifier (which has a much lower voltage drop than a rectifier tube).
Packs quite a wallop of watts for such low heater power. Great for 10Wrms of clean-ish power, up to 15W for 'crunch-ier'
Similar threads
