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Heaters wired in parallel?
Heaters wired in parallel?
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Old 17th July 2018, 08:23 AM   #1
cal16v is offline cal16v  Australia
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Default Heaters wired in parallel?

Hi Folks,

I bought a Raphaelite DSK6L 6L6 GC single-ended amp second hand and the documentation *I think* shows the heaters to be wired in series but the amp I have seems to be in parallel, via 2 sets of 6.3V taps from the transformer.

I found the first pic and diagram online and my unit is the last pic.

Which is correct?

Appreciate any help forthcoming here

Many thanks!
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File Type: jpg DSK6LZHP.jpg (574.9 KB, 205 views)
File Type: jpg Raphaelite.jpg (138.3 KB, 204 views)
File Type: jpg 20180717_141846.jpg (980.0 KB, 193 views)
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Old 17th July 2018, 09:26 AM   #2
Alan4411 is offline Alan4411  Wales
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They are all the same, both pairs of valves are in parallel as is shown on the first 'drawn' picture. (If they were in series they would only receive half the heater voltage each.)
What makes you think otherwise?

Alan
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Old 17th July 2018, 09:53 AM   #3
cal16v is offline cal16v  Australia
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Hi Alan,

I'm not used to reading schematics but in the diagram does not V2's supply piggy-back off V1 and likewise V4 off V3?

I could be reading that wrong?

Thanks
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Old 17th July 2018, 11:53 AM   #4
Alan4411 is offline Alan4411  Wales
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No problem, hope this helps.

Use V3 and V4 as the example. (V1 and 2 are the same, but different pin numbers.)

Parallel connected.
Two ways to do it, first like your amp, feed each valve individually from the transformer 6.3v winding. Or like the 'schematic' take one pair of wires from the transformer to V3 pins 2 and 7. Then feed V4 from those by linking both their pins 2 and 7 together. Either way they are paralleled and both methods have 8 connections in total.

Series connected.
One wire from the transformer (6.3v) goes to V3 pin 7. V3 pin 2 is now connected to V4 pin 7. And V4 pin 2 connects back to the transformer 6.3v connection. If you look there is only one connection at each location so 6 in total.

The sketch tries to show the un-twisted schematic version, parallel, and what it would be if it was 'series' connected.

Alan
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Old 17th July 2018, 12:34 PM   #5
cal16v is offline cal16v  Australia
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Thanks very much Alan.

Your drawing cleared things up very well.
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Old 17th July 2018, 04:33 PM   #6
DAK808 is offline DAK808  United States
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Heaters wired in parallel?
Almost all PP type amps use parallel heater wire connections. Sometimes there are 2 or more filament circuits. 1 for the power tubes and 1 for the preamp tubes. There is also different ways to make the connections but the end result would still be the same. If all the heaters measure at 6.3 more or less i would not worry about it. Unless, you are having a problem with hum from the heater lines?
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Old 17th July 2018, 10:17 PM   #7
cal16v is offline cal16v  Australia
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Another question...

The OPT's in my unit have a ground wire mounted to the chassis whereas the 'schematic' does not show any grounds whatsoever...

I presume this is correct, they should be grounded to the chassis?

Thanks
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Old 18th July 2018, 01:13 AM   #8
PRR is offline PRR  United States
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Quote:
Originally Posted by cal16v View Post
....I presume this is correct, they should be grounded to the chassis? ...
Yes.

A) User safety. If the transformer insulation failed, 400V wants to go to the exposed speaker terminals and the user messing with them. A grounded secondary will limit the voltage to almost-none, and typically something else will burn-up quick, removing danger.

B) The amp appears to have NFB. There are green wires from secondary to a switch to a resistor network, probably under the first cathode. This won't work unless the other side of the secondary is also referenced. The drawing shows a black wire from both zero terminals to the power board and from there to the heart of the amplifier. There are several ways this could have been done, and your build may do it different in mechanical detail, but same intent.

Also: To ground or not to ground the OPT secondary, that is the question

Last edited by PRR; 18th July 2018 at 01:15 AM.
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Old 18th July 2018, 01:23 AM   #9
cal16v is offline cal16v  Australia
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Quote:
Originally Posted by PRR View Post
Yes.

A) User safety.
Thank you PRR. This is my priority of course

Just a noob question if I may...

The switch is labelled Triode / Pentode. Difference?
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Old 18th July 2018, 05:42 AM   #10
PRR is offline PRR  United States
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> The switch is labelled Triode / Pentode. Difference?

I was gone blind working out that wire-diagram.

OK, NFB is disconnected in triode, connected in pentode. Naked (no NFB) triodes are quite listenable, naked pentodes are awful brash/bright/barky and want NFB.

Since you might use it in pentode w/NFB, and anyway need the ground for safety, they just ground it.
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