Problem adding reverb to a 5f2a

[Brebar]

Hello, I am trying to add reverb to a 5f2a amp that I built. The reverb circuit is from an aa764. Anybody have any ideas where to hook this up?

Here's the back story. I hooked the reverb circuit onto the 5f2a as shown in the schematic below. It did not work. The amp was cracking and popping through the speaker and I could hear a regular clicking noise coming from the 6v6 area, probably an arcing 6v6. I checked the bias resistor voltage drop and found that it was fluctuating between 1v and 3v about every 2 seconds or so. Without the reverb circuit the Vd was 32 volts and the amp sounds great.


Thanks.

5f2a reverb.pdf

[Phil_S]

Look at something like the AA1164 for some hints on how to do this. It looks to me like you have the out/in between the preamp tube and the 6V6. V3B looks to me like it is not properly configured and I don't think you need it. Put the out/in after to .02u coupling cap between the two original triodes. You'll need to figure out where in relation to the tone pot you want to place it, but the "in" needs to feed into the grid of the second triode.

I see you are new here. Welcome to TAG. Good luck with your project.

[Brebar]

Phil thanks for the tips. I was wondering if I needed the other half of v3. I interpreted the use of the other half of V3 in the aa1164 as necessary to the circuit, guess not.

Question about the V3 tube, you said it was not configured correctly, is that because there are two grid leak resistors shown, a 470k and a 220k? I'm going to remove it, I'm just curious.


It'll take a couple of days to report back after I try your suggestions.

Thanks Again!

[Ten Over]

This may be what you were thinking of.

[Brebar]

Yes that's what I was thinking!! Wow..... thank you so much for the drawing and your time to amend my drawing. I may take a couple of days to rewire the circuit, but I will let you know what happened.

So it's confirmed...... I can add a spring reverb to a 5 watt amp?

[Stevem]

Just note that the added current draw out of the power supply to run both sides of that 12AT7 pan driver it will likely make your 5 watt amp into a 3 watt amp!

Also you need to confirm that your filament voltage does not drop below 6.1 VAC when you connect up that added tube.

If that filament voltage drops below 6.1 your power transformer will start to run hot and drag down the V+ voltage also.

[Ten Over]

Just note that the added current draw out of the power supply to run both sides of that 12AT7 pan driver it will likely make your 5 watt amp into a 3 watt amp!

Also you need to confirm that your filament voltage does not drop below 6.1 VAC when you connect up that added tube.

If that filament voltage drops below 6.1 your power transformer will start to run hot and drag down the V+ voltage also.

Both sides of the 12AT7 combined are drawing less than 4mA. The added 12AX7 brings the total additional current to around 6mA. The output power isn't going to notice the difference.

He has enough heater juice for six small bottles and a 6V6.

[pdf64]

Yes, the PT is suitable for a Princeton Reverb!

[Brebar]

Yes the Hammond 290ax is the same PT I used in a Princeton Reverb build. I also calculated the current needs as follows:
Heater current. Plate current
6v6 450ma. 30ma

(2) 12ax7. 600ma. 4.8

12at7. 300ma 20ma

Total. 1.35A. 54.8ma



Hammond 290ax

5v HTR = 3A
6.3 HTR = 2.5
High voltage = 100ma

The 290ax should be able to handle the addition of two extra tubes.
Thanks for the replies. I'll let you know what happened.

[Brebar]

Ten Over, A few questions....

I have never seen a 3900 ohm 1w or a 11k ohm resistor before. I'll have to search Amplified Parts.

I see that you're recommending using point C (387v) to feed the reverb driver instead of 432v point B. The schematic says +400v on the plate of the 12at7, any reason for the lower voltage?

The only reason I'm asking is because I'm still learning about amps. I've built 3 of them and restored another, but that does not make me an expert by any means. I'm just pretty good at following schematics and wiring diagrams, kind of like a monkey with a soldering iron, LOL. This the first time I have deviated from the schematic. So if I ask stupid questions please forgive me.

Thanks for your help and have a nice Labor Day!

[Ten Over]

Ten Over, A few questions....

I have never seen a 3900 ohm 1w or a 11k ohm resistor before. I'll have to search Amplified Parts.

I see that you're recommending using point C (387v) to feed the reverb driver instead of 432v point B. The schematic says +400v on the plate of the 12at7, any reason for the lower voltage?

The only reason I'm asking is because I'm still learning about amps. I've built 3 of them and restored another, but that does not make me an expert by any means. I'm just pretty good at following schematics and wiring diagrams, kind of like a monkey with a soldering iron, LOL. This the first time I have deviated from the schematic. So if I ask stupid questions please forgive me.

Thanks for your help and have a nice Labor Day!

3900 and 11K are both E24 values. AES has 3.9K @ 1W, but no 11K @ 1/2W. Odd because they have 110, 1.1K, and 110K. I'm pretty sure I bought some 11K's from them earlier this year. 10K or 12K will give a HT voltage that I would consider acceptable.

The screen node (Point C) is a common place to connect the reverb transformer. There is more filtering there and the voltage hasn't dropped much from the plate node. Whatever voltage winds up at point C will be plenty for the reverb driver.

[Brebar]

Thank you all for your advice! IT WORKS and sounds great. The schematic that Ten Over provided did the trick. How ever I did not have in stock the 3900 ohm or the 11k ohm, those will be put on order. I left the originals in, I hope that doesn't affect anything.

The amp had a problem with squealing, I unplugged the tank and it went away. I plugged it back in and placed it as far away as the wires allowed and placed a towel over it.
The squealing was gone. So Leo was correct and put the reverb tank in a bag!

Thanks again.

[Brebar]

I have since come to the conclusion that this circuit is not the way to go. Way too much gain from the extra 12ax7. Eliminated that 12ax7 and tied the reverb, in and out, to just after the tone stack. Works perfectly!!