#124 Questions

[rootz]

I'd think when you follow the standard layout, you'd avoid grounding problems. Hmmmm... Checked if the heater AC is exactly symmetric?

[Bombacaototal]

...

[Bombacaototal]

Great! Many thanks again. I will leave as is.

One question on the wiring of the speaker jacks. On the layout of #124 it looks like the grounding of the 2 jacks are jumpered together, even if the jacks are grounded individually to the chassis.

Is the best approach adding the extra lead jumpering the grounds of each of the two jacks together?

The safest way is with a ground jumper between the two jacks. Just in case one of the jacks would loosen from the chassis, you'd still have connection to the OT secondaries. If it were to become disconnected while pushing signal through it, your OT would be at risk. Just one short wire goes a long way towards peace of mind.

Many thanks Dorrisant and Martin for the explanations. I had wired with the jumper so no need to amend that!

Ground loop sorted. I had jumpered the two output jacks and added an extra lead to the power tube ground and this was my ground loop! I removed both the jumper between the jacks and the one to the PT ground

[Bombacaototal]

I had my latest amp in a head shell for some time, but can’t remember that I had a hum from nearby PS components like you do.

Some questions. Is that reverb pan grounded in some way? Does the hum get less when you place a jumper between the amp chassis and the pan? Does the hum get less when you put a metal cover over the underside of the pan (make it a closed box; ground the plate)? Is the hum 60 cycle? Any difference when you replace the shielded cable to the reverb by something different?

The reverb pan itself is grounded on the input (black). As mentioned on the previous post it was originally on the return side but I had to move it due to the ground loop.

It made no difference by adding an alligator clip in the pan and chassis. I tried a different rca cable too

Attached a recording of the hum and a pic of how I have the pan sitting on a wood bar and the sleeve and the copper foil I used between the pan and the transformers

Back at this. Doing further testing while I await for the muMetal. So I removed the jumper connecting the output speaker jacks ground on this amp too. And I started experimenting with 2 different reverb pan, one grounded at black (input) and another grounded at the output (red). The input (black) grounded one will pick up a lot of interference from the PT but on the output grounded (red) the noise is present but is less pronounced. The issue now with the output grounded (red) is an additional high pitch continuous hiss even with the pan outside of the head, but when I touch the pan it goes away.

[Bombacaototal]

Marcus, a question for you, which fuse do you use on your 100W?. Mine has about 450V on the 6L6 plate and I have a 2A fuse, but I blew one this week with the amp master at Max and Volume at Max for some time (was burning it in). I wonder if I should go 2.5A? Or if I have a different issue

[xtian]

Marcus, a question for you, which fuse do you use on your 100W?. Mine has about 450V on the 6L6 plate and I have a 2A fuse, but I blew one this week with the amp master at Max and Volume at Max for some time (was burning it in). I wonder if I should go 2.5A? Or if I have a different issue

Yes, go with 3A slow for a 100w amp.

[Bombacaototal]

Marcus, a question for you, which fuse do you use on your 100W?. Mine has about 450V on the 6L6 plate and I have a 2A fuse, but I blew one this week with the amp master at Max and Volume at Max for some time (was burning it in). I wonder if I should go 2.5A? Or if I have a different issue

Yes, go with 3A slow for a 100w amp.

Thanks Xtian, and just t be sure I am in Europe running 240V on the PT.

[xtian]

Marcus, a question for you, which fuse do you use on your 100W?. Mine has about 450V on the 6L6 plate and I have a 2A fuse, but I blew one this week with the amp master at Max and Volume at Max for some time (was burning it in). I wonder if I should go 2.5A? Or if I have a different issue

Yes, go with 3A slow for a 100w amp.

Thanks Xtian, and just t be sure I am in Europe running 240V on the PT.

Oops, thanks for the reminder. 3A is overkill at 240v. You may have an issue with your amp!

[talbany]

Fender Twin type uses 4A slo fuse for 120V, 2A slo for 230 and 240V, 100W
I wouldn't go above a 2.5A

BTW
Was your transformer getting hot??
Tony

[Bombacaototal]

Fender Twin type uses 4A slo fuse for 120V, 2A slo for 230 and 240V, 100W
I wouldn't go above a 2.5A

BTW
Was your transformer getting hot??
Tony

Hi Tony, I’ve been always running it at 2A but only once I blew it, not sure what happened to be honest, but my pilot (which is running at 240V from the mains ) went at the same time.

I am using a power conditioner and a brown box to keep the mains voltages just below 240V.

I will check the PT next time this happens. My bias is slightly above 50% (fairly cold)

For a 50W should I use 1.5A? Thats what I’ve using but wondering if I should take it down to 1A

[talbany]

Depends on the transformer? Normally you should be able to take it down to 1A on a 60w? However, if it blows on power-up you may need to take it to 1.5 to allow for some in-rush current from the windings and caps charging up. If you start blowing 1.5's after the amp is charged then something's not right?

BTW. If the PT doesn't get real hot and it continues to blow chances are it's a tube going bad? if not check your tube sockets next for any carbon traces left around pin 3 for any arching. If so you're going to have to remove that carbon otherwise it will continue to arc there and blow the fuse. These are some common problems I check for.


Good lucK!

Tony

[Bombacaototal]

Depends on the transformer? Normally you should be able to take it down to 1A on a 60w? However, if it blows on power-up you may need to take it to 1.5 to allow for some in-rush current from the windings and caps charging up. If you start blowing 1.5's after the amp is charged then something's not right?

BTW. If the PT doesn't get real hot and it continues to blow chances are it's a tube going bad? if not check your tube sockets next for any carbon traces left around pin 3 for any arching. If so you're going to have to remove that carbon otherwise it will continue to arc there and blow the fuse. These are some common problems I check for.


Good lucK!

Tony

Thank you very much for the reply Tony. My 50W has a ClassicTone Bassman style PT. I have been running it at 1.5A and never blew a fuse. Will take it down to 1A and see if it is fine.

As far as the 100W with the ClassicTone Twin style PT, I will leave it at 2A, and will surely check PT heat and PIN3 for carbon if it blows again.

Wondering also if folks here use a second fuse for the PT CT. Mine is going straight to ground but have been thinking if I should add it

[erwin_ve]

Changing the mains fuse in 230-240v 50Hz territory isnt simply half of the USA 120v 60hZ.
The frequency from 60hZ to 50Hz has a bigger current draw. Because: Z= 2*pi*f*L
For a 50w in 230v-50hZ use a 2A sloblo.
For a 100w in 230v-50Hz use a 3A sloblo.

[talbany]

Changing the mains fuse in 230-240v 50Hz territory isnt simply half of the USA 120v 60hZ.
The frequency from 60hZ to 50Hz has a bigger current draw. Because: Z= 2*pi*f*L
For a 50w in 230v-50hZ use a 2A sloblo.
For a 100w in 230v-50Hz use a 3A sloblo.

Erwin
We already went over this
https://ampgarage.com/forum/viewtopic.p ... hilit=fuse

Tony

[erwin_ve]

Changing the mains fuse in 230-240v 50Hz territory isnt simply half of the USA 120v 60hZ.
The frequency from 60hZ to 50Hz has a bigger current draw. Because: Z= 2*pi*f*L
For a 50w in 230v-50hZ use a 2A sloblo.
For a 100w in 230v-50Hz use a 3A sloblo.

Erwin
We already went over this
https://ampgarage.com/forum/viewtopic.p ... hilit=fuse

Tony

I know, living on the 50Hz side has gained me real life situations. Yet I see the advise take 1/2 of the rating and then being surprised the fuse blows without finding a cause.