tube amp reverb question

[dschwartz]

hi all.. i´m building a tube amp using parts from a fender pa100..the hole amp is sounding OK (i mean, great!) but now is time to put the reverb in..

i made an fx loop wich goes from the preamp follower to another gain stage..
i have only a 12at7 for the reverb circuit..i made a gain stage with half 12at7 and connected the output to a reverb mix control (250k A pot) and then to the fx loop gain stage, and connected the output of the reverb springs to it, specting to hear reverb if i move the springs.. but i only could hear a very faint reverb, even with the rteverb mix at max..

any idea how can i make a reverb circuit to add it to the amp?

ps: a have a spair 12ax7 triode..

[petemoore]

  Schematic or partial would help..I can't quite follow what you have there.
  And the 6g15 is the reverb I used to help fashion a reverb.
  But I'd take a look at a Fender amp w/ reverb, or browse the 18w forum's reverbs, and other amp build sites.
  The split on 6g15 is right at the input, the 'bottom' line [clean] goes through a buffer/to 1 side of mix pot.
  The reverb tank needs enough current to drive it [12at7 should be good] and enough voltage swing too, also needs to be impedance matched to the tube output.
  Then 1/2 of a triode for recovery.
  Driving the reverb is basically an amp output. Haven't studied other Reverb in Amp circuits with triode output, but there are two gain stages and then the EL84 getting the signal 'up' to drive the tank.
  The recovery stage is 1/2 a triode [1 gain stage], but could be something else...
  As could I think the input triode gain stage, being as it's handling smaller signals...
  The last two lines were written because I 1/2 get the idea you are a gain stage or so short.
  I was 'there' recently, thinking of Mosfet power tranny or other type of active to help operate the reverb.
  VOX I have does it with IC's, and has a 36v tap on the transformer to run them.

[drewl]

There's a reason Fender used a reverb transformer in their tube amps.
You need to drive a low impedance tank, so alot of current is needed.
That's why amps without a reverb tranny use a power tube to drive the tank, or you could use a tank with a higher impedance.
paralleling the 12AT7 might get you enough current to drive the tank.
look up some old amp schems like Silvertone, or some gibsons or other cheapo amps to see different reverb circuits.

[JFX09]

I don't know if any of this can be of some use to you, but it's there anyway: http://www.accutronicsreverb.com/schemat.htm

something here perhaps: http://ozvalveamps.elands.com/reverbs.htm

[dschwartz]

Thanks for the links guys, but those are SS reverbs

i´m not worried about the driver yet. It is a full tube reverb..i have the parts from a fender pag120, that means a reverb transformer, a 12at7 tube ( and a spare preamp triode) , and an accutronics reverb tank  that i couldn´t find the model number, but it´s made to be used with a reverb transformer..

i wanted to make the circuit from output to input, validating that the output of the reverb tank would sound on the amp if i hit the springs..it worked, but like crap..just too faint, almost imperceptible.

i boosted the output of the tank with a 12at7 gain stage (400V B+, 220K anode R, 270R/10uF cathode to ground, 3,3nF 2kV coupling cap, to mix pot and directly to the input of the FX loop recovery gain stage)

what sould i do? better use the 12ax7 triode as gain stage and piggyback the 12at7 for the driver?

i was basing my reverb to the mesa boogie mark IV reverb, assuming that they use very similar to fender parts..This reverb has 1 12at7 gain stages before an after the reverb tank (with a transformer)..

any thoughts

[petemoore]

  The recovery stages 12at7's Tube input should accept reverb transducer output as source, and provide some gain.
  Run the recovery stage output into a guitar amp [ie into preamp/amp] and it should sound the loud clanging of reverb when you touch and rattle the springs.
 

[dschwartz]

that´s what i wanted to probe..since the FX loop recovery stage is a preamp itself..
i´ve seen that the PA100 has a 1.5M/22pF trough the audio path, and a 470K from the reverb path.. as mixing resistors..rather than boosting the signal a lot, it lowers the dry signal a lot and mix with the wet at a 3 to 1 balance..

but could that lower the output volume of the amp? too much? (it surly lowers it)..