#124 Questions

[Bombacaototal]

I had a bit of a bunkers idea, to have the 2 different voltage options for an amp, a higher voltage which would be “stock” and a lower voltage option which would add an additional dropping resistor in series probably right after the PI.

Question (i) will I need a mains type switch to withstand the voltage at that part of the circuit (ii) would there be any issues in using his switch with the amp ON (for the 9Pin tubes for example). Would I expect to have big pops when using the switch?

The underlying rationale is that the ODS amps use the large 22K dropping resistor while SSS amps are a bit more aggressive with lower values. So I was thinking of how to make it possible to have both options with a switch

[pompeiisneaks]

High voltage DC switches tend to be pricier as switching higher voltage DC is hard on a switch. I'd recommend highly that you not switch it with the power on, as it can cause arcing and cause loud pop's etc when it hits the speakers. It would likely almost be safer to have a low voltage switch operating an SSR instead. I don't know what kind of those may work best in audio setups, (If at all).

Someone may know a good switch designed for that high level of DC voltage switching, nothing I'm searching for comes up but 500$ ones for industrial use.

~Phil

[talbany]

I had a bit of a bunkers idea, to have the 2 different voltage options for an amp, a higher voltage which would be “stock” and a lower voltage option which would add an additional dropping resistor in series probably right after the PI.

Question (i) will I need a mains type switch to withstand the voltage at that part of the circuit (ii) would there be any issues in using his switch with the amp ON (for the 9Pin tubes for example). Would I expect to have big pops when using the switch?

The underlying rationale is that the ODS amps use the large 22K dropping resistor while SSS amps are a bit more aggressive with lower values. So I was thinking of how to make it possible to have both options with a switch

The only thing that comes to mind would be a Mercury Wetted relay. They actually come in an octal form.
WARNING!. I have never used them don't know how they will perform?? or voltage handling .Your on your own.
https://www.surplussales.com/Relays/mercury.html

Tony

[Bombacaototal]

Thanks Tony and Phil. Yes looks like this might be a gamble so I will scrap this idea, although it would have been cool.

Another idea I had is to put the presence cap and pot on a switch which could bypass them. Any issues in using a normal 2 way mini toggle for the PI cathode?

[pompeiisneaks]

the cathodes generally run at a lower voltage. you'd want to know for sure the operating range of your specific amp, for example cathode followers tend to have higher cathode voltages etc. I'd get some max DC voltage readings to make sure the switch is rated, but it should be much more doable yes.

~Phil

[dorrisant]

Not trying to argue, but the PT is the biggest concern for proximity issues. EMF radiation is the biggest pitfall. I have had to rebuild a few amps that were not that well thought out... no, not my builds. A couple of cases where a guy was trying to build like Trainwreck. Not Ken's circuit but his build style, with PT and OT on the same end of the chassis. When he put them in a combo cab they would not clear the speaker. OTs were moved to the other end, very close to V1 and V2. They didn't pick up any extra noise. They were both crazy high- gain JCM800 type things, so the extra gain should have exaserbated the issue but did not. I have built plenty of amps where I had to mount the OT where I had to and hope for the best. Never had a problem with it yet. Of course I always try to pay attention to all of the noise reduction tricks I can, I'm sure that helps prevent some of the problems I've read about.

EMF from PT is the biggest problem, chokes seem to be a distant 2nd, then OT. I'm sure if you routed preamp and OT wires in parallel you will have issues, but attention to wire routing gets you through a lot of issues.

Like Tony said, aluminum will not sheild EMF much at all, steel is much better and mu metal is the best. Generally you have to encase the offending object in mu metal for the most effect... and do bend it too sharp. Those sharp corners and edges start to defeat the whole purpose.

Best defense is proper spacing, 2nd is lead dress and location. Those are much easier to control.

[Bombacaototal]

For the Rock/PAB/JAzz would any of these 2 work?

https://uk.rs-online.com/web/p/toggle-switches/7347050/

https://uk.rs-online.com/web/p/toggle-switches/7347202/

[martin manning]

No, On-Off-On is what you want.

[norburybrook]

No, On-Off-On is what you want.

that was my first thought but I think he's wanting to have a 3 way switch Martin with PAB in the middle, is that on-off-on still?


M

[martin manning]

Yes, correct.

[Bombacaototal]

Thanks Marcus and Martin. Indeed I am looking for a 3 way switch with the PAB in the middle but tha ks for clarifying that a on/off/on is what I need

[Bombacaototal]

So my vintage Fender pots cannot fit the M8 smooth washer. Any issue in going pot -> star washer -> chassis -> locking nut?

[norburybrook]

I can't see any problem with that.

M

[Bombacaototal]

Thanks Marcus

[Bombacaototal]

On Output Transformer: HAD usually places the wire holes further down the chassis, one close to the output jack and the other closer to the power tubes. Taylor and Two Rock on the other hand make a hole right underneath the OT and then distribute the cables internally on the chassis. This means that the primaries and secondaries of the OT will most likely be under the board.

The benefits for using HAD approach is that you can assemble everything and leave the OT for last and also in the situation of a repair.

Any preferred approach at TAG? I am thinking of going as per Taylor to make it more tidy.