Starting a D'Lite

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Structo
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Re: Starting a D'Lite

Post by Structo »

This is probably a stupid question but you did ground the HT center tap right?
Tom

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dreric
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Re: Starting a D'Lite

Post by dreric »

This is probably a stupid question but you did ground the HT center tap right?
Tom (when it comes to this stuff I am stupid)

Here's scan of the power transformer specs and here's how I have them hooked up

Primary 120 / 120 to the outlet

Secondaries

1st coil 640v, 250mA center tapped

Red 320v = one side of the rectifier

Black / Red center tap 160v = Bias

Red 320v = Other side of the rectifier

2nd coil 6.3v, 4.8A center tapped

Brown 3.15v = heaters

white / brown center tap = ground

Brown 3.15v = heaters

3rd Coil 5v, 3A

Yellow 5v = relays

Yellow 5v = relays

It seems to me that having all of my diodes be bad is unlikely, can anyone see a wiring issue that is evading me? Should the 640 center tap be grounded and the 6.3 center tap be the bias?

Thanks

Eric
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Bob-I
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Re: Starting a D'Lite

Post by Bob-I »

The black/red and white/brown need to be grounded. I don't know why you have black/red liste4d as bias, it's not a bias tap. This xformer doesn't have a bias tap so you'll have to use one of the red legs to the bias supply and adjust the values of the resistors.
talbany
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Re: Starting a D'Lite

Post by talbany »

Bob-I wrote:The black/red and white/brown need to be grounded. I don't know why you have black/red liste4d as bias, it's not a bias tap. This xformer doesn't have a bias tap so you'll have to use one of the red legs to the bias supply and adjust the values of the resistors.
+1 That transformer CT GROUNDED!! should give you 451V Plates.. Like Bob said that transformer doesn't have a bias tap so you will need to add one off the HT side of the sec.. Here is one Henry gave me that works fine you may have to adjust the 52k to ground but works great... Good Luck

Tony
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dreric
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Re: Starting a D'Lite

Post by dreric »

that transformer doesn't have a bias tap so you will need to add one off the HT side of the sec..
you'll have to use one of the red legs to the bias supply

I apologize for my ignorance and I am grateful for the help.

I don't understand the quote above (HT=?). Do I take a tap from one of the 320v say from the junction of the secondary and the diode and run it into the bias supply. Wouldn't that give me 320v going into the bias when it wants to see 45v. So I would have to increase the value of the resistor from 470 ohm to ?

Thanks

Eric
talbany
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Re: Starting a D'Lite

Post by talbany »

dreric wrote:
that transformer doesn't have a bias tap so you will need to add one off the HT side of the sec..
you'll have to use one of the red legs to the bias supply

I apologize for my ignorance and I am grateful for the help.

I don't understand the quote above (HT=?). Do I take a tap from one of the 320v say from the junction of the secondary and the diode and run it into the bias supply. Wouldn't that give me 320v going into the bias when it wants to see 45v. So I would have to increase the value of the resistor from 470 ohm to ?

Thanks

Eric
Do I take a tap from one of the 320v say from the junction of the secondary and the diode and run it into the bias supply.
Yes..

The 56K resistor shunts AC to ground.. The lower the value Greater the drop..Bias supply's draw very little current.. Find the resistor value that gives you the 48v or close then hook up the cap.. You can also do a Marshall or Trainwreck style bias supply although I like this one the best not as spongy!!.. Good Luck..FWIW.. This supply was also used in Sundown amps..

Tony
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Structo
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Re: Starting a D'Lite

Post by Structo »

HT I believe is a hold over from years gone by, it means High Tension or high voltage.
It usually refers to the secondary voltage of a tube amp power transformer.
I kind of thought maybe the center tap was not grounded correctly by your symptoms.

As others have said, your PT does not have a bias tap, so you have to create one from the 320v winding.
Tap off of it like shown and you should be good to go.

Remember that the bias voltage is NEGATIVE, so the diode and cap have to be reversed with the + towards ground for the bias diode and filter cap.

Don't forget to ground the white/brown center tap for the 6.3vac heater supply as well.

You can use the 5v tap to power your relays.
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Structo
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Re: Starting a D'Lite

Post by Structo »

Also B+ refers back to the days when actual batteries were used to power tubes.

Here is a simple drawing for the bias circuit.

Remember that you will have to adjust the 56K to give the desired range of 20-45mv or ma bias on the 1 ohm resistors on the cathodes of the power tubes.
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dreric
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Re: Starting a D'Lite

Post by dreric »

Tom, Tony, TM, Bob & everyone else ......................

THANK YOU!

Eric
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Re: Starting a D'Lite

Post by CHIP »

Structo wrote:This is probably a stupid question but you did ground the HT center tap right?
Wasn't such a stupid question after all. :wink:
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dreric
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Re: Starting a D'Lite

Post by dreric »

Hi guys

I made the bias supply as suggested. Now measuring (sans power tubes) from the wiper lug of the bias pot I have a range of -18.4 to -37.9 dc volts as I adjust the pot. I am unclear as to what the range should be ans whether I need to adjust the 56K resistor or if I am in good shape. Suggestions?

Grounding the center tap brought all the voltages up, in fact they are about 15 volts higher everywhere when compared to the d-lite voltage charts. Is this OK?

When I put in the power tubes, all controls on minimal settings "1" I get a loud high pitched whine, not leave the room loud but lets just say that I don't have to clean my ears tonight. The pitch of the whine changes as I manipulate the bias pot. Changing the settings on the volume, tone, OD and master doesn't affect the whine but the whine is affected by the presence pot; getting louder, changing pitch then going to a motor boat , aliens landing kind of sound.

All help is greatly appreciated

Eric
ampdork
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Re: Starting a D'Lite

Post by ampdork »

Haven't read the whole thread so not sure if this is helpful but your current symptoms sound like you have the OT primaries reversed.
If so you will get positive feedback instead of negative....then you get oscillations like your hearing and presence control is in feedback network so I'd look there.

Typically, but not always (some odd irons out there) when your looking down into the amp with the rear panel towards you the blue OT lead goes to the pair or single power tube on the right side, the brown lead to the left side.

Good luck, HIH.
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Structo
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Re: Starting a D'Lite

Post by Structo »

Yep sounds like the old OT switch a roo.
If your OT primary wires are too short to reverse, you can reverse the wires that go from the power tube grids to the 220K .1uF on the board.
Tom

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dreric
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Re: Starting a D'Lite

Post by dreric »

Okay

+2 on backwards wiring. Seeing that I am such a pro at wiring a transformers I thought I'd show how it's wired before I trash something.

Here's the spec sheet. I thought I was wiring it so that I could switch between the two ohm ratings thus being able to switch between 6V6 and KT66.

So how ass backwards have I done this one? :shock:

Thanks

eric
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Structo
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Re: Starting a D'Lite

Post by Structo »

Looks right to me.

I had my D'lite wired like that for a while but I never tried 6V6 in it.
So later I removed the switch but put in dual bias pots.
I like that arrangement and I can run tubes a bit closer together or as far apart as I want.

As far as the bias range, when I bias my 6l6 to 42ma the bias voltage is
-48v.

For 6V6 I think you want around 22ma? Can't remember.

You have a different PT so I can't advise what change you need to bring it closer to the range you need.

I think for 6V6 you need around -37v.
That would give 19ma on the cathodes.

Here is a D'lite 22 6V6 voltage chart. I suggest a range in bias between 18ma and 22ma.
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Tom

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