Layout - Feedback wanted!

[überfuzz]

Hi!

I've been posting several posts regarding an amp that is going to be a mix between a Bassman and a Carvin. The layout is finally starting to look like... well let's say something, for now. The chassi is somewhat gnarly, no room between the tube sockets and the pots. Not enough room between the back side and the tubes. This made me split the board in two. See the picture!

Questions

1. I have a lot of 0.056 and 0.04 caps in my stash. This circuit has got 0,047 in several places. Do I mess it up completely if I go with my 0,04 and 0,056 caps, like in the phase inverter. If no, which is to prefer..?
2. Ehh... I guess that's it for now.

Feel free to comment, cheers for now!

Layout

[JoeM]

Do you have a schematic for this amp?

[überfuzz]

Well sort of... I based it on the carvin 33 circuit. One channel is kept more or less unchanged. The other channel was dismissed and replaced with a bassman 5f6a circuit. From the input jack, channel one is the carvin channel and number two is the 5f6a channel.

In this layout I've added a negative feed back potentiometer to it.

[defaced]

1. I have a lot of 0.056 and 0.04 caps in my stash. This circuit has got 0,047 in several places. Do I mess it up completely if I go with my 0,04 and 0,056 caps, like in the phase inverter. If no, which is to prefer..?

Depending on the tolerance of your caps, if you had an 0.047 the tolerance may be wide enough to grab 0.040 and 0.056. It doesn't make a whole lot of difference which one you choose, in that small of a range I'd mark it up to personal taste. I'd opt for the 0.040 personally to slightly limit bass over the 0.047.

And I agree with Joe, if you want a critique of the amp, we need a schematic. Layouts are great for building, but horrible for analysis.

[JoeM]

Really difficult to tell what's going on with the layout. Is this really related to physical layout of the amp? For example, you have an input on the right side, which is nearer (physically) to the EL84 outputs, and then a long distance going to a 12Ax7. I think you need to rethink a layout that makes more sense in relation to the actual circuit.

[überfuzz]

Joe - Actually, that has kept me awake during the nights. (Well figuratively speaking at least.) See the first post about the chassis. The tube sockets are really jammed together, the PT and the OT are in the opposite side of the chassis. This layout seems to give the shortest signal way. Speaking in terms of all signal wire; tone control, OT - tube, etc. There are some DC wiring going out throughout the chassis, but I don't think they're going to cause any noise, hum. If the power tubes are causing a lot of noise I probably have to move the power tubes sockets all together. But I think I'll try this first.

defaced - What you write sound comforting. I might be wrong here, but let me go a bit off topic here. RI versions of old classics are often a bit harsh in their tone. This has lead me to think that point to point wiring with vintage components are filtering some of the high parts of the tone. The same circuit with modern hifi components with a nifty pcb board don't filter. So the old circuit which techs designed to balance the old vintage stuff sounds harsh.

Like you said, using the smaller caps, 0.04, would probably push it a bit towards a more trebled tone... Should work with both the vintage part of the amp, that would be the 5f6a part, and the more modern part. However, if the 5f6a turns out to be to high or treble sounding I'll try the 0,056...



If you like to comment of the scheme I could pencil it down for you.

[JoeM]

The chassi is somewhat gnarly, no room between the tube sockets and the pots. Not enough room between the back side and the tubes. This made me split the board in two

OK, so you're using an existing chassis? Any pics of that? Maybe you're trying to cram too much into it. I'd rather have simple amp that works, than try to do too much and just end up with a nightmare of problems.

[defaced]

I'm on typing on my phone so this going to sound kinda curt. If I were to tailor high end id find some discrete way to do it like a cap to ground in the preamp. The pi coupling caps have more to do with how much low end is passed than limiting high end.

[überfuzz]

Joe - Chances are that you're calling attention to something here... I've been thinking a lot about this circuit, whether it's going to be to crowded or not. My final conclusion was GO, try it, but don't be surprised if someone throws a I hate to say I told you so right in your face.

defaced - No I was merely talking about which effect the different caps would have. I'm not trying to tailor the tone in any way. My hope is that the circuits will do that just fine.

[JoeM]

Joe - Chances are that you're calling attention to something here... I've been thinking a lot about this circuit, whether it's going to be to crowded or not. My final conclusion was GO, try it, but don't be surprised if someone throws a I hate to say I told you so right in your face.

I'm not trying to throw cold water on your project (so to speak). But I am baffled by the location of the input jacks in relation to the output tubes. That's why I asked for a chassis pic. I would be sure you understand how signal flows in this, and also a proper grounding scheme (at the very least). Otherwise you could have oscillation and hum issues.

[überfuzz]

Joe - I believe I do. But as you were saying. The tube sockets are placed somewhat... ill. They're all eight in row, very close, approximately 1 cm apart.

If I look at the different schemes. Bassman 5f6a and carvin 33 there's a misch-masch of linear and logarithmic potentiometers. How about this: log pots to; bass, mid, treb, volume and linear pots to reverb and presence?

Cheers!

Edit, a linear to bias pot maybe. :-)

[JoeM]

I built a 5F6A clone. Uses log for the treb and bass, and linear for middle. No reverb on mine, but I'd consider a log taper, on most Fenders the reverb comes up fast, so it may depend on how your circuit is designed. I dont have presence, it has a fixed resistor and cap instead. You definitely want to use a linear for the bias pot.

[überfuzz]

I've started the hands on work now. You asked for pictures and here's one. I guess you can spot most of the stuff. We debated the positioning of the tubes. The power tubes are situated at the right and the pre amp tubes are 1 to 4 from left. With this layout I get some room between the power tubes and signal wires. The front board and the face pots will be somewhat jammed together but I think it'll be ok. Is it a good call to move the front board in the position it is in the picture, or could I place it closer to the power tubers. More to the right?


About the 0.047 caps. I actually have loads of 0.0068 caps in my stash. If the 0.04 caps are cutting to much bass my first attempt to fix it will be bypassing the 0.04 caps with a 0.0068 cap. It won't look good but hey. Ctot = C1 + C2 + ... in parallel caps.