Tweed Overdrive Special

[10thTx]

Is there much difference between this amp and the schematic posted above?

The schematic and layout are Geezer's amp & that was his playing on the two clips you mentioned.

With respect, 10thtx

[mat]

I hope that this is not too silly question but would it be possible to design the circuit to use an EL84 instead of the 5879 ? I read somewhere that the EL84 can be used also as a preamp tube.

This circuit as it is now has really caught my ears. I like the sounds of the clips very much. I'm going definitely to build some version of the TOD maybe with the one tube reverb.

Thanks,

[10thTx]

hope that this is not too silly question but would it be possible to design the circuit to use an EL84 instead of the 5879 ? I read somewhere that the EL84 can be used also as a preamp tube.

I don't know the answer, but I would be surprised if you could do that.
Many "new' ideas in amp designs are simply recycled and/or rearranged versions of something done in a previous amp that was successful.

For example, some Gibson amps used 5879 pentodes in a preamp.

So my question would be ........ can you show me a successful and good sounding guitar amp that uses an EL84 in the preamp? And if not, perhaps there is a reason for that.

with respect, 10thtx

[Alexo]

I think the main reason not to use an EL84 in your preamp is that it is ridiculously inefficient - say 75ma idle current for a gain of maybe 25. not to mention the big ol' power resistors you'd need for plate load and RK.. Unless you use some really funky looking voltages and loads to try and make it act like a preamp tube, but by that point,t he sonics will be very different.

You could use one to drive a phase inverter interstage transformer though if you really wanted to.

[Cliff Schecht]

Like others said, as a preamp tube that's a wasteful endeavor. The only time you see tubes like an EL84 or EL34 as "preamp" tubes is when they are being used to drive high power tubes like the 2A3 or 300/A/B tube types. Other than that, it's not so much innovation as it is a waste of a good part. In other words, unless you have a specific reason why you want to use an 84 that way, it's probably a waste of time, money and effort.

[Zippy]

I recall a 6BQ7 in the reverb circuit of the Traynor YGL-Mk III. That was my gigging amp of the early '70s.

[Cliff Schecht]

6BQ7 is a dual triode and a good candidate for a reverb driving stage. Had to look that one up .

I think the original question has gotten confused. The 5879 is a preamp tube specifically meant for low noise, high gain applications. An EL84 is a purpose built audio power pentode, meant to be able to dissipate some heat on the plates before burning up (good for driving speakers).

The difference between a pentode and a triodes sound is really dependent on where it is used. Pentodes are more efficient amplifiers (on the order of 5x or more) and tend to be very linear and bright. This is due to a few things, one being a lower miller capacitance allowing for more highs to come through and another being a lower plate reistance meaning less dampening. Pentodes can sound brighter than triodes in a similar situation because of these factors. I've found that pentodes don't sound so good when pushed into distortion in a preamp stage though, they can have some goofy issues and don't distort so musically when clipped hard. There are some pentodes that sound pretty good when clipped though, my old Silvertone from '54 uses a 6SJ7 as the sole preamp tube (grid leaked like the old Champs) and it does a pretty cool dirty sound, even when pushed.

Power stages are a different story and usually aren't pushed into a ridiculous amount of distortion. This causes a lot of third and will make the amp sound less musical after a certain point.

[mat]

Thanks for the answers. Guytron seems to use two EL84's on the preamp section: http://www.amptone.com/guytrongt100.htm

The reason for asking if the EL84 would do is that the 5879 is not so easily found in this part of the world I live. The delivery will be about 3-9 weeks from USA.

EF86 is more easily available and JJ's EF806S are on production today. Have anyone tried the JJ or would that be suitable for the TOD ?

Thanks,

[10thTx]

Guytron seems to use two EL84's on the preamp section

As I understand the Guytron amp ........... the "preamp" is like a complete amp in itself in the preamp section (think like a Vox with two EL84's) that goes into a power amp that is 100 watts.

So the EL84's are not used in a V1 preamp position as we normally think of preamp tubes.

Compare the tube data of the EF86 and the 5879. My guess is you might be able to make that work, but you'll probably have to change some things? The EF86 has more gain than the 5879 does.

With respect, 10thtx

[mat]

Thanks for the info 10thtx. I'm going to wait for the 5879 then. I would like the amp to sound exactly like Yours.

[David Root]

5879 has a unique pin-out, but if you've heard an old Gibson GA-40, that's what's in them (except the '54).

I think this new design has a lot of merit just on paper, and the clips prove it out!

How about a 4x6L6GC/EL34 with Twin PT and a Marshall 100W PT? I smell ZZ tonez maybe?

[mat]

Compare the tube data of the EF86 and the 5879. My guess is you might be able to make that work, but you'll probably have to change some things? The EF86 has more gain than the 5879 does.

With respect, 10thtx

Ok, I started to take apart my D-build (2xEL34, built in loop,HRM+nonHRM OD sections). I'm going to build the Tweed OD. I ordered 5879 tubes but it might take couple of months to get them so I purchased an EF86 tube to build the amp with that first. I noticed the different pin layout of the EF86 and 5879. Is there anything else to consider when building the TOD with EF86 ?

I'm very exited of the build. The sound clips of the amp are just what I'm after.

Thanks,

[10thTx]

Mat,

I've never had or built an amp with EF86 tubes. So in light of that, I'd probably just build it the same (except pinout) and then if needed you can parallel resistors across the drive or level pots to reduce gain.

Looking forward to hearing how you like this amp! I'm loving mine.

With respect, 10thtx

[mat]

Mat,

I've never had or built an amp with EF86 tubes. So in light of that, I'd probably just build it the same (except pinout) and then if needed you can parallel resistors across the drive or level pots to reduce gain.

Looking forward to hearing how you like this amp! I'm loving mine.

With respect, 10thtx

Thanks 10thtx, I'll build it the same and try also lowering the gain with parallel resistors.

Btw. Have You tried Your build with pedals, does it take them in a good way ?

[mat]

When looking at Svetlana EF86 datasheet there are pin 1 screen grid, pin 8 supressor grid and pin 9 control grid. How do they relate to 5879's pin 1 G1, pin7 G2 and pin 9 G3 ?

Thanks,