Weird Heater Supply Problem - And other solutions!

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Littlewyan
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Re: Weird Heater Supply Problem - And other solutions!

Post by Littlewyan » Wed Oct 18, 2017 5:41 pm

I don't think swapping the primaries would have hurt. In fact it shouldn't have made any difference.

Have the heater secondaries got a centre tap? Or are you using resistors to create ground reference?

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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Wed Oct 18, 2017 6:42 pm

Yeah, I would think it wouldn't damage the PT but, I figured I would mention it.

The heaters do not have a center tap. So I had to create one with 100 ohm jobbers to ground. I will recheck all of my wiring and pull it off the tube sockets and test for the correct voltage.

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Re: Weird Heater Supply Problem - And other solutions!

Post by Littlewyan » Wed Oct 18, 2017 6:51 pm

Yeah double check the 100ohm resistors. Do you read 6.3V if you put your meter leads across the secondaries rather than from one side to ground?

Do they read the same without valves?

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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Wed Oct 18, 2017 10:24 pm

Littlewyan wrote:
Wed Oct 18, 2017 6:51 pm
Yeah double check the 100ohm resistors. Do you read 6.3V if you put your meter leads across the secondaries rather than from one side to ground?

Do they read the same without valves?
The resistors are good. I just double checked and I get 6.5 vac across the secondaries. Then I test from one side to ground and I get 2.7 vac and 3.8 vac on the other.

This is with the secondary artificially center tapped but not wired to the sockets.

Strange!

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Re: Weird Heater Supply Problem - And other solutions!

Post by neikeel » Thu Oct 19, 2017 4:28 am

Sounds good, how about HT?
Neil

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Re: Weird Heater Supply Problem - And other solutions!

Post by Littlewyan » Thu Oct 19, 2017 4:58 am

It is weird but personally I wouldn't be overly concerned about it. As long as it doesn't go higher than 6.5VAC. Have you tried different meter settings? Like voltage limits just in case it's reading a bit funny?

And yeah what neikeel asked.

I'm actually in the process of tweaking my Marshall Master Volume 20W amp at the moment so will be interesting to see what you do with your amp :)

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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Thu Oct 19, 2017 11:36 am

The HT is fine. What I don't understand is why the imbalance exists now when it didn't before I fired up the amp.

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Re: Weird Heater Supply Problem - And other solutions!

Post by neikeel » Thu Oct 19, 2017 12:17 pm

As long as your heaters are 6.3vac +/-10% you will be fine with your virtual centre tap.

Are you getting around 490v dc after the rectifier now?
Neil

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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Thu Oct 19, 2017 1:17 pm

I guess I figure it would be bad to have one side of the tube's heaters getting 2.7vac and the other 3.8vac. I am getting 535vdc after rectification.

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Re: Weird Heater Supply Problem - And other solutions!

Post by Littlewyan » Fri Oct 20, 2017 8:30 am

Yeah I see what you're saying about the heater voltage. Isn't the heater circuit often out of balance anyway? When people install those humdinger pots to get rid of hum, aren't they adjusting the balance of the heater voltage?

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Re: Weird Heater Supply Problem - And other solutions!

Post by neikeel » Fri Oct 20, 2017 9:23 am

The heaters will get the 6.3vac between the pins as long as you have the centre tap arrangement you describe, the imbalance has effectively been taken out by joining them with the 100Rs so you can forget that.

535 is a bit high for EL34s but most will cope, make sure you have at least 1k on the screens of each socket. It may drop lower when the tubes are in, drawing juice and biased up properly.
Neil

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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Sat Oct 21, 2017 1:47 am

Alright! The amp is up and running. I am surprised how dark the amp is and it has tons of low end. I am running 6L6s so I think that's a lot of it.

I tried installing the bright cap but it didn't make a lick of difference.

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Re: Weird Heater Supply Problem - And other solutions!

Post by Littlewyan » Sat Oct 21, 2017 5:14 am

Great! You sure it's dark? Mine takes my head off!!! Completely stock 2203 preamp?

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Re: Weird Heater Supply Problem - And other solutions!

Post by marshallnoise » Sat Oct 21, 2017 10:59 am

Yeah it was completely stock. I have done some tinkering already. I need to recheck my values I guess. I used the Cerra Tone 2014 guide as my template. It has the bright cap removed on their layout.

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Re: Weird Heater Supply Problem - And other solutions!

Post by Littlewyan » Sat Oct 21, 2017 6:42 pm

Ah that'll be it. Try the bright cap, see what you think :)

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