Cascaded 12ay7 for non top boost channel

[mauiboy81]

Greetings and salutations!

I am wanting to use a 12ay7 to get close to the gain of an ef86 for the non top boost channel in a top boost style amp I am building. I don't have any ef86 and want to try something different.

I have tried the single triode with volume control like vox as well as going with parallel triodes. They both sound great and have their place but obviously have little gain and are nowhere near the ef86. I also have found that the tone is just like the top boost with the eq set flat.

I have a bunch of 12ay7's around and have always loved how they sound in tweeds..... So what if I cascade one 12ay triode into the other and send that straight to the pi?

I could use a fixed voltage divider between the stages and volume before the pi or I could have the volume between the two stages. I kind of want to use a 6 pos tone switch like on many of the ef86 preamps. Do you think this would be better between the 12ay7 stages or after the second stage before the pi?

Any thoughts?

Take 'er easy

[chief mushroom cloud]

I would just try the two gain stages...but in this fashion
1st stage pre = Vox normal ch setup>
into cap switching setup (a-la /13 as in their ETR30)>
500kA vol pot>
Vox follower amp w/o the follower part (100ka, 1.5kk, 25uF bypass)>
a cap = to largsest cap used in the previous switching scheme>
either a) another 500kA pot or b) a 220k buildout resistor

If you are familiar w/ voxes...this is pretty straightforward

Tweek values in 2nd gain stage to suit the drive characteristic you are looking for....

suggestion: use 4.7-5uF cathode bypass caps.....it actually sounds punchier
don't use Marshall/Fender power supply scheme...they're retarded...use distributed fanout from screen supply


just had another idea....put a 10-12k resistor at the bottom of the first vol, and use a 2nd 500k vol pot after 2nd gain stage...you would basically have a 'Normal' preamp w/ the first vol all the way down, and you can dial up 'drive' w/ it if you want.

[mauiboy81]

Well, I went ahead and did it. I patched it into a test amp I have.

I'm using 100k plate and 1.5k cathode resistors. The bypass cap on the first stage is 22uf and the second stage has 1uf. I have a cap switch and 1MA volume between the stages and a cap switch and 500kA volume before the pi. I have a 220k/220k voltage divider going to the pi because in the final amp i will be mixing the top boost channel and this channel there. I will take the reverb from after the mixing resistors and return it on the other side of the pi.

I need to mess with it and find what values i like but it sounds pretty cool. Even with the first stage volume all the way up the second stage 12ay stays clean. All the distortion comes from the pi. I have to turn up the volume after the second stage to get any clipping. I only want one of the volumes and one cap switch so I need to figure out which one to replace with fixed values.

[mauiboy81]

Thanks, chief!

I'm not familiar with the /13 you referenced.

I was planning on using the fender style power supply.... as i am adding this to a rocket with reverb. why do you no like this type of power supply?

[chief mushroom cloud]

Thanks, chief!

I'm not familiar with the /13 you referenced.

I was planning on using the fender style power supply.... as i am adding this to a rocket with reverb. why do you no like this type of power supply?

I'm just kidding about the FenMar power supply....I like the fanout because you can control each gain stage B+ and there's less interstage interaction to the B+...but they are what they are and that contributes to their character...
I thought you were building vox-ish amp...the reverb adds complexity...and not to mention it's a Rocket, to boot.....
I know a Rocket is a TB variant (albiet WAY overfiltered w/ a FenMar power supply topology, but that's what makes it a Rocket!)...but it would be interesting to see how you implement this reverb circuit like you describe.....

sorry, I'd like to add that using a switchable range boost in front of a 'stock' Normal preamp...does the same thing.

[mauiboy81]

Have you used or built one of those /13's? How does it sound with the reverb mixed across the 3.3M but without the recovery stage?

The reverb I was going to implement would be something like what you see in the lightning reverb or chieftan schematic.

I guess what I'm doing is as voxish as any of those top boost/ac15/30 variants are.

[chief mushroom cloud]

I built the /13 pre-amp into my AC15FROMHELLVARIANT...and it rocks...but I have not put reverb into builds (there's only one reverb circuit in an amp I like...Sano 160R). I can't say that I've heard a Chieftain reverb, but I like the way they implement it...if that's what you're up to...I think it's a good idea.

btw...is there a Lightning Reverb sch flying around? I didn't know on existed.

[mauiboy81]

Here is the lightning reverb

https://tubeamparchive.com/download/file.php?id=13171