Help with boutique amp I have acquired.

[markusb111]

A good friend of mine passed away and I was gifted an amp he built himself. I am not sure if it is a kit he assembled or how he came about the design. When I took it it had an external cabinet plugged into the 1/4" jack instead of the 10" speaker that was on board. It's hard to see but there is a long thin toggle switch to the left of the far right vacuum tube. As it isn't labeled I am assuming it is an impedance switch but am not sure. Can anybody recognize this configuration and perhaps shed some light for me? I have posted a few pics and will try and get a closer shot if need be. Does anybody recognize this configuration? Any idea what switch does that is highlighted? Thanks a million for any help in advance. There are two Mallory 150 0.047 at 630VDC Tube Amp Capacitors on either side of the toggle. How's that for sounding like I know what I am talking about? Found pics of them on Google Image Search. Other dumb question for a newbie. Does it matter if tubes are upright in an amp or upside down as in this configuration?

[stratele52]

This an home made amp , from a kit ? i don't know .

But the swith is IMO a boost switch . I work by changing bypass capacitor on a preamp tube's cathode.  Try to move the switch , sure you will hear more or less "crunch" / overdrive or less clean.

Tubes upright down ; no problem , all Fender amp and many other are built like that .

Bigger photos will help

[markusb111]

Thanks for the reply. My friend passed away so I can tell you that the cabinet is rough but I can't tell if it is a kit or not. That's one of the questions I am putting to the forum. It is a three way switch and the capacitors on either side are exactly the same. That is why I thought it wasn't a boost. I am a guitar player not an electrician so you could be correct. The funny part is that I live in an apartment so firing this thing up is problematical  I will post some closer pics. They were larger but I couldn't get all four up because I had exceeded size limit. Guess I will have to do multiple posts but didn't want to break any rules as am a newbie. Thanks again.

[stratele52]

You could firing switch at low volume , the boost it is not 100 watts trust me .

[markusb111]

Adding more pics per request.

[markusb111]

More

[markusb111]

To stratele52. It does indeed boost the signal. I was so afraid to push it! If this were a switch to change the ohms on the speaker plugged in would that also make a volume difference at low volumes? Outboard cabinet had two speakers one horn and one 12", cabinet in enclosure has one 10" speaker. Okay now for the biggest question. Should I cover the back of the metal chassis as I was told there is a danger of high voltage shock with the electronics exposed?

[PRR]

> Should I cover the back of the metal chassis

YES!!

If you (or your cat) stick a finger (or nose) in there, it can be lethal. If it tips agains a metal beer-keg or similar, sparks can fly, magic smoke escape, it stops working, and clearly you are not yet ready to begin repairs.

If his room is still cluttered, look for a panel just that size. Chassis are usually sold with bottoms (back in this position), pre-punched for screws. That would be the cleanest fix.

If his shop has been cleared, at least get some 1/4" plywood, mark, drill, screw.

[markusb111]

Thanks for the reply. My cat passed away a while ago so luckily I am the only critter here. His shop is closed and I didn't see anything that resembled a cover so I will go and purchase a piece of plywood. Do I need to keep some of the back open like on a Marshall? Another thing I noticed is that he built the 1/4" jack to plug in the speaker between two of the large tubes (you can see this in the pic) and I assume that if that wire sits against either it will be hot enough to melt the insulation. I am happy for the gift and it sounds great but I want to be safe too.

[alerich]

There are two Mallory 150 0.047 at 630VDC Tube Amp Capacitors on either side of the toggle.

It is a three way switch and the capacitors on either side are exactly the same. That is why I thought it wasn't a boost.

One of the caps on that switch is clearly a .022uf. The switch possibly changes an interstage coupling cap value if the other cap is a .047uf.

[markusb111]

Thanks, my eyes are not the best. That makes sense as that is why there is a boost when the toggle is flipped. Two correct answers to my question abut toggle switch. I welcome the help.

[HotBluePlates]

The problem with the pictures is that it's hard to see what the caps are connected to. Knowing that would likely tell us what they do in the cirucit, which would clear up what their function is.

[stratele52]

There are two Mallory 150 0.047 at 630VDC Tube Amp Capacitors on either side of the toggle.

It is a three way switch and the capacitors on either side are exactly the same. That is why I thought it wasn't a boost.

One of the caps on that switch is clearly a .022uf. The switch possibly changes an interstage coupling cap value if the other cap is a .047uf.

No.
Interstage capacitor named coupling capacitor do not boost signal . I clearly see the center lug of the switch go to a groung buss . Never a coupling capacitor is connected like that. These capacitors use here must going to a 12XX7 cathode ( pins 3 or 8 ) with a "more " standard capacitor value like 25MFD polarized. But photo are not good to be sure.
I built some amps like that for a boos switch

[stratele52]

PRR is right .  You must close the back , lethal voltage.

For the back of your cab , here what is you could built with 1/4 inches quality plywood ; the 2 holes you see is to vent the tubes and the wood around , to protect tubes and to not touch them .  Electronic chassis are completely close.


http://www.amprestoration.com/wp-content/uploads/2011/03/april-19-2011-092.jpg

[floyd]

Here are the cover plates for your Hammond chassis box...http://www.tubesandmore.com/products/enclosures?sort=recommended&page=1&filters=Type%3DSteel%20Chassis

[stratele52]

Here are the cover plates for your Hammond chassis box...http://www.tubesandmore.com/products/enclosures?sort=recommended&page=1&filters=Type%3DSteel%20Chassis

Yes it is an option if you can not do basic woodworking. But IMO better to make a standard back panel for the same price or less than the Hammond cover.

[alerich]

No.
Interstage capacitor named coupling capacitor do not boost signal . I clearly see the center lug of the switch go to a groung buss . Never a coupling capacitor is connected like that. These capacitors use here must going to a 12XX7 cathode ( pins 3 or 8 ) with a "more " standard capacitor value like 25MFD polarized. But photo are not good to be sure.
I built some amps like that for a boost switch

Yes.
Increasing the value of the coupling capacitor will absolutely result in more signal in the form of increased lower frequencies being sent to the next stage.

The center lug of that switch appears to be going not to the ground buss but to one of the control pots. White inner insulation with yellow outer covering (perhaps yellow cloth wire with teflon inner insulation). If it's going to a gain control that even lends more credence to the coupling cap theory.

.022uf and/or .047uf capacitors seem awful small for a cathode bypass cap. Adding .022uf or .047uf to a 25uf cap (or even a 5uf cap) would have a negligible impact. The tolerance of the main bypass cap is probably more than that.

We are in agreement that we need better pictures.

"How do you feel about Cleveland?" 

[alerich]

Thanks, my eyes are not the best. That makes sense as that is why there is a boost when the toggle is flipped. Two correct answers to my question abut toggle switch. I welcome the help.

Instead of switching between a .022uf and a .047uf a better implementation of that is to hard wire a .022uf in place and then switch another .022uf in parallel for a total of .044uf when you want the boost. That way the signal is never interrupted and there is no pop from the switch.

[stratele52]

Yes.
Increasing the value of the coupling capacitor will absolutely result in more signal in the form of increased lower frequencies being sent to the next stage.

Not more signal ( millivolts ) but more or less frequency

[sluckey]

Changing the cap value changes the capacitive reactance and that will change the signal level as well as affect the tone. But maybe this switch is not about boost but rather more intended to be a tone switch, similar to the Vox circuit?

[stratele52]

Changing the cap value changes the capacitive reactance and that will change the signal level as well as affect the tone. But maybe this switch is not about boost but rather more intended to be a tone switch, similar to the Vox circuit?

Without better picture or shematic ( forget it ) we can't say more.

[alerich]

Yes.
Increasing the value of the coupling capacitor will absolutely result in more signal in the form of increased lower frequencies being sent to the next stage.

Not more signal ( millivolts ) but more or less frequency

A bypass cap does the same thing. Larger cap = lower frequency.

[stratele52]

Yes.
Increasing the value of the coupling capacitor will absolutely result in more signal in the form of increased lower frequencies being sent to the next stage.

Not more signal ( millivolts ) but more or less frequency

A bypass cap does the same thing. Larger cap = lower frequency.

No bypass cap ...bypas +/-cathode  resistor of tubes and drive more the tube . Coupling cap don't do that.

[markusb111]

Thanks, my eyes are not the best. That makes sense as that is why there is a boost when the toggle is flipped. Two correct answers to my question abut toggle switch. I welcome the help.

Instead of switching between a .022uf and a .047uf a better implementation of that is to hard wire a .022uf in place and then switch another .022uf in parallel for a total of .044uf when you want the boost. That way the signal is never interrupted and there is no pop from the switch.

I truly can see that without better pictures this won't be easy but I believe that I can genuinely say 1. There is no pop when switch is thrown. 2.Both of them look like they are .022uf. 3.There is a significant volume boost when switch is thrown even at very low volume. 4. I am grateful for the help especially in making sure I don't fry my amp or myself!  

[alerich]

It was just an educated guess. First they were both .047uf. Now they are both .022uf. PRR gave you the best advice in this entire thread. Make a back cover, install and stay out of the guts of that thing.