Best practices for chassis layout...

[1blueheron]

Could someone please correct if I have any of these layout principles wrong.

1.  PT as far from Pre-amp input and first gain stage as possible and AC power cord, on/off switch, and fuse, power indicator light adjacent.
2.  Rectifier tube as close to PT as possible.
3.  Output tubes next
4.  Phase inverter next
5.  Any FX, reverb or trem circuits, loops or intermediate gain stages between preamp and phase inverter
6.  Keep all wiring leads as short as possible but still maintainable/repairable.


Items in question...

1. Where is the best place for filter caps?  PT end or Preamp/input end.
2. Where is the best place for OT?  PT or Preamp/input end.
3. What wiring should be twisted and what wiring should be left straight.
4. When should tube heater jackets be used?
5. Is a standby switch in amps beneficial or just extra trouble?
6. Where/when should EMI shielding be used?
7. What should co-ax be used for and not used for.

Thanks in advance.

[shooter]

A picture is worth a 1000 words;

http://sluckeyamps.com/november/november.htm

study what the 'ol guys here have done, replicating that does take awhile 

[SoundmasterG]

Could someone please correct if I have any of these layout principles wrong.

1.  PT as far from Pre-amp input and first gain stage as possible and AC power cord, on/off switch, and fuse, power indicator light adjacent.
2.  Rectifier tube as close to PT as possible.
3.  Output tubes next
4.  Phase inverter next
5.  Any FX, reverb or trem circuits, loops or intermediate gain stages between preamp and phase inverter
6.  Keep all wiring leads as short as possible but still maintainable/repairable.


Items in question...

1. Where is the best place for filter caps?  PT end or Preamp/input end.
2. Where is the best place for OT?  PT or Preamp/input end.
3. What wiring should be twisted and what wiring should be left straight.
4. When should tube heater jackets be used?
5. Is a standby switch in amps beneficial or just extra trouble?
6. Where/when should EMI shielding be used?
7. What should co-ax be used for and not used for.

Thanks in advance.

1. Filter caps should be close to the stages they are supplying...so not at either end of the amp but distributed among the circuitry.
2. OT can be placed in both locations, and there is a way to use headphones and the OT to determine best place for it before you wire amp up.
3. Heater wires should be twisted, but don't have to be. Power supply wires should be twisted.
4. Are you talking the preamp tube covers that Fender used or something else?
5. Players like the usability of a standby switch mainly for the muting feature, but standby is not needed in any tube amp that uses receiving tubes (i.e. any musical instrument amp) and in some cases it can be a problem.
6. Most amps do not use EMI shielding.
7. Co-ax could be used on inputs on the first stage, grid wires where the signal is coming into the tube. Only tie one end to ground if you do use co-ax. Many, many amps do not use co-ax and work perfectly fine.


Greg

[VMS]

I agree on all that Greg wrote above (maybe a fellow TUT books reader    )


Just one more thing to add, grid stopper resistors should be soldered to tube sockets.

[1blueheron]

Could someone please correct if I have any of these layout principles wrong.

1.  PT as far from Pre-amp input and first gain stage as possible and AC power cord, on/off switch, and fuse, power indicator light adjacent.
2.  Rectifier tube as close to PT as possible.
3.  Output tubes next
4.  Phase inverter next
5.  Any FX, reverb or trem circuits, loops or intermediate gain stages between preamp and phase inverter
6.  Keep all wiring leads as short as possible but still maintainable/repairable.


Items in question...

1. Where is the best place for filter caps?  PT end or Preamp/input end.
2. Where is the best place for OT?  PT or Preamp/input end.
3. What wiring should be twisted and what wiring should be left straight.
4. When should tube heater jackets be used?
5. Is a standby switch in amps beneficial or just extra trouble?
6. Where/when should EMI shielding be used?
7. What should co-ax be used for and not used for.

Thanks in advance.

1. Filter caps should be close to the stages they are supplying...so not at either end of the amp but distributed among the circuitry.
2. OT can be placed in both locations, and there is a way to use headphones and the OT to determine best place for it before you wire amp up.
3. Heater wires should be twisted, but don't have to be. Power supply wires should be twisted.
4. Are you talking the preamp tube covers that Fender used or something else?
5. Players like the usability of a standby switch mainly for the muting feature, but standby is not needed in any tube amp that uses receiving tubes (i.e. any musical instrument amp) and in some cases it can be a problem.
6. Most amps do not use EMI shielding.
7. Co-ax could be used on inputs on the first stage, grid wires where the signal is coming into the tube. Only tie one end to ground if you do use co-ax. Many, many amps do not use co-ax and work perfectly fine.


Greg

Greg,

1. So is it better to use smaller size, individual caps and distribute them vs. the larger multi-tap caps?  If using the larger multi-tap ecaps, where would you put them?
2. Can you elaborate or point me to reference on the headphone OT location technique?
3. Thanks for clarifying.  Got it.
4. I have seen numerous preamps using metal tube shields.  Have read they serve 3 purposes, speeding warmup time,  stabilizing operating temp and shielding from EMI/RF.  Some seen in Fenders but mostly on Hi-Fi and test gear equipment. Anything to this or mythical legend.
5. Concurs with my research, just wondering why so many people install them.
6. I have seen both metal covers or foil used under the chassis of audio gear as well as metal partitions between PT/Rectifier section and the rest of the tubes.  Seems like a cheap, low tech method of reducing possible noise but doesn't seem widely used in guitar amps.
7. Users choice ehh?

Thanks for the feedback!

Shooter,

Sluckeys Nov. amp has a layout that I could pretty closely replicate on my project.  Good reference.  Thanks.
Organ amps are the bulk of my exposure so far.  One of them put the OT next to the PT, the other did not.  One had filter caps next to the preamp section away from PT, the other put them near the PT.  Both used foil shield under the chassis. 

Trying to avoid any potential problems when drawing this up.

[PRR]

There is no "perfect".

"Better" is in the eye of the bee holder.

There is always some mistake nobody ever thought of.

[SoundmasterG]

Greg,

1. So is it better to use smaller size, individual caps and distribute them vs. the larger multi-tap caps?  If using the larger multi-tap ecaps, where would you put them?
2. Can you elaborate or point me to reference on the headphone OT location technique?
3. Thanks for clarifying.  Got it.
4. I have seen numerous preamps using metal tube shields.  Have read they serve 3 purposes, speeding warmup time,  stabilizing operating temp and shielding from EMI/RF.  Some seen in Fenders but mostly on Hi-Fi and test gear equipment. Anything to this or mythical legend.
5. Concurs with my research, just wondering why so many people install them.
6. I have seen both metal covers or foil used under the chassis of audio gear as well as metal partitions between PT/Rectifier section and the rest of the tubes.  Seems like a cheap, low tech method of reducing possible noise but doesn't seem widely used in guitar amps.
7. Users choice ehh?

Thanks for the feedback!

1. It is better in all cases to use discrete caps (individual caps) rather than can caps that have several caps in the can. The reason for this is because can caps having several caps in the can end up sharing the grounds, and this is often a bad decision as it ruins the grounding system in the amp. If you have a dual section can cap you can use both sections in parallel and then the shared grounding doesn't cause a problem, but it is still cheaper to use discrete caps instead of the can. The only time I use cans is if the project I am working on is space limited and a can would come in handy, and then I will wire the sections in the can in parallel to control the grounding. With discrete caps distributed throughout the circuits located close to the stages they are supplying, you can optimize your grounding and control it so you don't get ground loops or hum into the sensitive circuits such as the amp input stage or a reverb stage. The second reason to use discrete caps is cost. Can caps cost much more than discrete caps of a similar value and are also less readily available these days since they are no longer as widely used in TV's and other consumer electronics like they were when the classic tube guitar amps were made in the 50's and 60's.
2. OT Headphone location trick >> http://ax84.rru.com/FAQs/general.html#ot-place
3. YW
4. There might be some to it, but I've used them or not used them on amps and all the amps worked fine and sounded fine either way. Try it and see.
5. Inertia and Expectation. So many people grew up with standby switches on their guitar amps and had no exposure to other tube equipment without one that they just expect that their amp should have a standby switch. It is useful for the muting function, but there are other ways to get a mute on an amp besides using a standby B+ interrupt switch like many classic amps use. Having a standby switch is fine though if you want it, it just isn't necessary, and if the amp is left in standby for long periods of time without being played it can damage the tubes.
6. The metal covers and foil under the chassis can help to reduce hum for sure. Its a good idea to incorporate it in a design, but make sure it actually grounds to the chassis when the chassis is installed in the head or cabinet or it has no benefit.
7. Yes pretty much. There are certain locations where it is a benefit, such as the input of the amp or other sensitive grid locations in the amp like a reverb stage, but using it on the plates has very little benefit for example. Lower gain amps such as most Fenders don't benefit much from it but in higher gain designs like a Mesa Dual Rectifier it would be a huge help on the inputs. Try it and see, but just make sure to only ground one end or you set up a ground loop.

I agree on all that Greg wrote above (maybe a fellow TUT books reader    )


Just one more thing to add, grid stopper resistors should be soldered to tube sockets.

Yes, the TUT series are excellent books with many great ideas. Likewise Merlin's books and website are great too. For beginners Dave Funk's Tube Amp Workbook (out of print now) was very good too, and the large full page Fender schematics are handy.


Agree with the grid stopper resistors. I like adding a minimum of 10k at the sockets as Kevin O'Connor suggests as I think it improves the sound overall.


Greg