new build choice, 2nd gen 50w

[Matt J]

Matt, I drew up a couple of nothing-but-rock layouts for Marcus a while ago, and they are posted here somewhere.

Marcus, for the FET you need a jack with an additional switch contact on the sleeve or ring contact, or one with an isolated switch like a 13E.

Awesome! Thanks, Martin!
I'll have to look for them and check them out. I'm thinking of trying that type of 2nd Gen build after I finish up my Trinity OSD kit.
- Matt J.

[norburybrook]

Question for you all;

If I went with the 4/5 pin footswitch socket, so I could use two relays and have one for the FET, I wont need the extra FET jack. There's only one Manual/pedal switch on this amp on the front panel, how would that work with an OD and FET two footswitch?



Marcus

[martin manning]

As suggested above, you could use a pull-switch type pot (replacing the trimmer on the FET board), located in the FET jack position for the manual/pedal FET boost. The pull switch would be wired the same as the rear panel switches that control the relays, and the actual FET/No FET signal path would be controlled by a relay.

[norburybrook]

would it matter though if it didn't have a 'manual' switch? I mean I'd always use it with a footswitch.

Also, how much current is flowing through there? can I use a guitar pot? a 10k Lin push pull is very rare it would seem. I've found a small gtr one;

https://www.ebay.com/itm/POTENTIOMETER- ... xyaTxRXaB1



M

[martin manning]

That'll work fine. You'll have to add something to center it in the 3/8" hole; I suggest an O-ring from the hardware store 8mm ID, 1.5mm thick, and a couple of thin washers so it's clamped to the chassis by the bushing nut.

[norburybrook]

Damn, I've just widened the hole for the cliff jack!!!

Should I use shielded wire going to and from the board?

Thanks Martin...you've changed your Avatar..very post modern



M

[pompeiisneaks]

Damn, I've just widened the hole for the cliff jack!!!

Should I use shielded wire going to and from the board?

Thanks Martin...you've changed your Avatar..very post modern



M

I would definitely use shielded for any runs longer than say an inch in that early of the input stage, otherwise you're asking for noise. In my FET the input and output aren't shielded but they're also right next to the jack. The run from the normal input then is shielded as it goes from there to the back of the amp. That's the most sensitive part of the amp, maybe aside from the OD section which has so much gain, adding noise is bad there too.

~Phil

[Mr. dB]

https://tubeamparchive.com/viewtopic.php?f=5&t=12113

[norburybrook]

Blimey! that was an interesting read....I can see there's a lot of food for thought there.

thanks, that will make for some interesting post build fiddling.

M

[Mr. dB]

One thing I've noticed about this 50W chassis is that it's cut for a Twin power transformer (3 3/4" x 3"), not a Bassman (3 1/2" x 2 3/4"). One is left with the choice to either use a transformer that fits, or cut a reducer plate.

Is there any particular harm in using a Twin-type power transformer in a 50W amp? The voltages are mostly the same, although the amp would draw about half the current the transformer was designed to deliver. I've seen this done in a couple of Small Special builds on this board.

I haven't measured the output transformer mounting holes yet...

[dbeasley]

One thing I've noticed about this 50W chassis is that it's cut for a Twin power transformer (3 3/4" x 3"), not a Bassman (3 1/2" x 2 3/4"). One is left with the choice to either use a transformer that fits, or cut a reducer plate.

Is there any particular harm in using a Twin-type power transformer in a 50W amp? The voltages are mostly the same, although the amp would draw about half the current the transformer was designed to deliver. I've seen this done in a couple of Small Special builds on this board.

I haven't measured the output transformer mounting holes yet...

There is no "harm" in running a bigger PT. I reckon there will be a difference in how the amp feels,especially when it's pushed hard - anyone whose ever hooked a bias probe up to a running amp and played a big fat power chord will notice that the power tubes can draw well over 120ma each in that initial attack/demand on the power supply. Less actual voltage drop under heavy demand maybe?

Sent from my Moto G (4) using Tapatalk

[norburybrook]

I've got a modified twin Transformer with an extra secondary for the relays. I've had to make a plate though as it was still too small for the Pre cut hole.

M

[norburybrook]

made my plate to mount the transformer and started to do some wiring after adding all the hardware to the chassis.

I've decided to put a half power switch on as I had a hole where the old ground switch was and I had a heavy duty DPDT switch that fit perfectly in there. Can someone explain how this works? as using a 100/50 half power you just lose two valves, in this case that's not possible. How do you get 22w switching from 50w on a pair of 6L6's?

I suppose it will be a 22/50w kind of thing. Might be interesting to dime it on the half power setting, who knows.

Couple of things I've noticed might trip me up.
1: there's no return on this amp in the layout, I have send and return on my chassis so am using both. I've wired it to the master volume(level) as per later models.

2; there's no separate level control for the OD so is that going to be tricky with the relays?

3; Is there any reason the wiring frpm the front mounted manual/pedal switch needs to go all the way around the perimeter of the chassis, rather than a short run directly under the boards?


i think that's it.

I'm going to try the FET trimer on the front with a push pull DPDT10k pot and have it switchable with a relay.

DSC_1652.JPG

DSC_1651.JPG

M

[dbeasley]

made my plate to mount the transformer and started to do some wiring after adding all the hardware to the chassis.

I've decided to put a half power switch on as I had a hole where the old ground switch was and I had a heavy duty DPDT switch that fit perfectly in there. Can someone explain how this works? as using a 100/50 half power you just lose two valves, in this case that's not possible. How do you get 22w switching from 50w on a pair of 6L6's?

I suppose it will be a 22/50w kind of thing. Might be interesting to dime it on the half power setting, who knows.

Couple of things I've noticed might trip me up.
1: there's no return on this amp in the layout, I have send and return on my chassis so am using both. I've wired it to the master volume(level) as per later models.

2; there's no separate level control for the OD so is that going to be tricky with the relays?

3; Is there any reason the wiring frpm the front mounted manual/pedal switch needs to go all the way around the perimeter of the chassis, rather than a short run directly under the boards?


i think that's it.

I'm going to try the FET trimer on the front with a push pull DPDT10k pot and have it switchable with a relay.

DSC_1652.JPG

DSC_1651.JPG

M

You could use a 3P3T to switch off 2 tubes, and switch the remaining pair from fixed to cathode bias. 3rd pole would switch the power tube grid leaks from bias voltage to ground.

Sent from my Moto G (4) using Tapatalk

[norburybrook]

this is what I'm using;

50w half power.jpg

just wasn't sure how it worked

M

edit: It's triode/Pentode clever stuff.