Prince Tremolo Reverb the 2nd

[Bitsleftover]

Hi
The bodge job 5f2a that i modded beyond recognition PT finally died so Im planning a rebuild
Its a 5f2a at heart which Im adding a one tube reverb and an AA764 tremolo circuit to.
Ive attached a layout and schematic.
If anyone has the time to look over them and give me any pointers or improvements I'd really appreciate it.
Thank you

 

[Bitsleftover]

 

[Bitsleftover]

 

[Bitsleftover]

I couldnt get a suitable 5y3 rectifier schematic symbol or a suitable PT symbol so please excuse the workaround.
Also im unsure where the best place is on the ground bus to attach the tremolo intensity pot and footswitch/speed pot jack grounds? Im thinking the Power tube Cathode Resistor ground?

 

[Lowerleftcoast]

I see a single point style ground bus but there is a back of pot connection on the tone and intensity pots.

 

[Lowerleftcoast]

Also im unsure where the best place is on the ground bus to attach the tremolo intensity pot and footswitch/speed pot jack grounds? Im thinking the Power tube Cathode Resistor ground?

Yeah, the 2nd filter cap.

The power for the reverb and trem should come from the next node up (higher voltage)(2nd cap positive terminal).

The trem cathode bypass cap could be larger (100uF). The trem works (and starts) by oscillating at low frequencies. The 25uF cuts off some of the lows, which sometimes delays how fast the trem kicks in.

I would put the preamp tube as V1. Less noise there.

 

[echuta13]

You could also use a led for bias in the trem section. The side benefit (besides bias and acting as a full bypass) is it lights up in step with the tremolo and reduces your parts count.
Could be mounted on the front panel in the trem section as and indicator.

 

[Bitsleftover]

You could also use a led for bias in the trem section. The side benefit (besides bias and acting as a full bypass) is it lights up in step with the tremolo and reduces your parts count.
Could be mounted on the front panel in the trem section as and indicator.

View attachment 920972

Thats really cool! I dont have space for it on the faceplate on this amp but Ill definitely try it in future. Thank you.

 

[Bitsleftover]

I see a single point style ground bus but there is a back of pot connection on the tone and intensity pots.

Good spot! Thank you

 

[Bitsleftover]

Yeah, the 2nd filter cap.

The power for the reverb and trem should come from the next node up (higher voltage)(2nd cap positive terminal).

The trem cathode bypass cap could be larger (100uF). The trem works (and starts) by oscillating at low frequencies. The 25uF cuts off some of the lows, which sometimes delays how fast the trem kicks in.

I would put the preamp tube as V1. Less noise there.

Ive redrawn it with a more traditional V1 Preamp topoligy and made the other changes you suggest. It just seems to use a lot more cable and a bit more back n forth this way. How does this look to you? Ive made a few other changes such as a safety earth that i missed previously.
Thanks for your help and input.

 

[Lowerleftcoast]

Imo, it is looking pretty good. Everything has trade-offs. Is it better to have a little more wire or to have the most sensitive tube further away from noisy bits? I can't tell you for sure which might be better. Ultimately it is your choice.

There is a school of thought to put the filter caps near the part of the circuit they service. You could move the 3rd filter cap with the cap's positive side terminating with the two plate resistors of V1. An alternate position of the mixing resistors would have to be considered.

An example of this would be similar to the optimized 5E3 layout from Rob Robinette's 5E3 Mods site:

 

[Bitsleftover]

Thank you for your help so far.
Ive moved that 3rd Filter Cap and shuffled things around for a slightly cleaner layout.
How does that look?
Where should I hook up the Preamp's ground bus? Point A or B?

 

[echuta13]

I would think Point B. Not sure it you will need to or not, but you may need another power filter stage to decouple the tremolo and/or the reverb circuit. If I was only going to add just one additional power stage, I would make sure it was for the tremolo circuit (an oscillator on its own stage could be a good thing).

Out of curiosity, do you use both inputs? I've found I generally only use one. Would save you some face space and parts if that's case.

 

[Bitsleftover]

That’s a very good point! I have a few amps with Hi and Lo inputs, and the Lo’s may as well not be there.
I’m thinking I could go Strats and Teles into High, and Les Paul into Lo.
Regarding adding another node… I’v been drawing upon the AA1164 Princeton for inspiration. I think that’s how its done there. If I really honest though…I’m not sure what the effect of the lack of a separate node would be.

 

[echuta13]

It may make a difference, it may not! The problem is you'll only find out after the fact!

I'm looking at Rob's page on the Princeton: https://robrobinette.com/AA1164_Princeton_Reverb.htm . It looks like the trem is hooked to the B power node, but there is a node that isn't being used unless my eyes are off. I would be inclined to move the trem down to the unused portion (still has decent voltage in that node!)

If you went with a multi-cap solution like the Princeton on Rob's page, it could also save some real-estate on your board...

I have a few amps with Hi and Lo inputs, and the Lo’s may as well not be there.
I’m thinking I could go Strats and Teles into High, and Les Paul into Lo.

I've use a first stage coupling cap switch in the past and I really liked it. It effectively trims the bass a bit, and by doing so cuts some gain. Works well for single coils in the Full setting (.022 cap), and the Firm setting (.0047 cap) works great for humbuckers. Kinda gives you a Fender/Vox tone change and isn't really just a "SC/HB" switch.

 

[Bitsleftover]

Robs site seems to have doubled in size every time I go back there. I’ll have a look. He’s probably got everything I need to know right there. Thanks

 

[EsquireBoy]

That is a really nice project!

I would personally consider putting NFB on a 5f2 circuit, unless you really want some dirt first and foremost.

Keep us posted!

 

[Bitsleftover]

That is a really nice project!

I would personally consider putting NFB on a 5f2 circuit, unless you really want some dirt first and foremost.

Keep us posted!

On it!
Thank you

 

[Bitsleftover]

That is a really nice project!

I would personally consider putting NFB on a 5f2 circuit, unless you really want some dirt first and foremost.

Keep us posted!

Ok...
The 5F2A adds 22k of NFB to the junction of the Cathode of the 12AX7 and its 1k5 cathode resistor. It has no Cathode bypass cap on V1B
The AA764 Vibrochamp has 2k7 NFB insterted between V1B's 25uf bypassed 1k5 cathode and its additional47r resistor to ground.
I intend to use a 3PDT switch to provide-
Up - Tremolo, alternate location 2k7 nfb with cathode bypass cap. (AA764)
Centre - No Tremolo, no NFB, no bypass cap.
Down - No Tremolo, standard placed 22k NFB, no bypass cap. (5F2A)

I've included this switch in the latest layout, and I have attached the preamp groundbus to the end of the remainder of the ground bus as one continuation. I have also moved the reverb mix resistor out of the way a little to accomodate.
Ive also added the termolo pedal to illustrate the on/off switch and speed pot with associated resistor.

 

[EsquireBoy]

No NFB with a cathode bypass cap would be an interesting option to have, since it’s the configuration that would give the most gain.

NFB vs no NFB makes a difference but I’m not sure the two options for the NFB location would be very audible.

I would go with a simple switch that disconnects the NFB.