Dc Heaters / What diodes and questions.

[RockinRocket]

Im going to get this Single preamp tube power transformer.

https://www.tubedepot.com/products/sing ... ransformer

Looking at the data sheet it shows a typical rectifier/filter ill be cut and pasting to start. The heaters are just Ac and was wondering what I should know to covert to dc. Ive looked at the Soldano supercharger schematic and will be cut and pasting there DC heater design. But it did not specify what diodes. Would 4 IN4007 do the trick? The transformer supplies 6vrms 300ma. Any thing else I need to know to do this? Thanks

[Stevem]

For far less than the cost of that filiment PT you can bias up the whole amps heater string if the heater feed is center tapped.
For non- high end Hi Fi use this will get you what you are looking for in hum reduction and you can just power off of the amps main B+ .
Oh, and yes 1n4007 are fine, just remember there 1 amp rating.

If you live in the US near a big city you may still find a radio shack open and they might still have a 120/12.6 volt transfomer on the rack and these have enough current to do atleast two 12 series triodes, and ćost less than that PT you posted!

[martin manning]

Anything else I need to know to do this?

Yes, lots. ;^)

The Soldano Supercharger schematic shows a typical full-wave bridge (FWB) rectifier circuit on the power transformer's heater winding, but the resulting DC is used only for energizing the relay coil. The heaters are AC powered.

The transformer you are considering has a 6.3VAC winding rated at 300mA. If you rectify that with a FWB and connect it to a 12AX7 tube, it will use 300mA DC. That means you will be asking 300/0.62 = 484mA from the transformer. That is some 60% above its rating, and it is likely to overheat and fail.

You could elevate the heater center tap with a voltage divider off the high-voltage DC, but with only 3 mA DC available there, you have very little, if any, to waste. The transformer is designed to power one 12AX7, which will use just about all of that. I'd recommend sticking with AC heater power. If you pay attention to the layout you won't have any problems with 60Hz hum.

[SilverFox]

I'm trying this circuit out. It worked in the Kustom and I'm using the Kustom's PT. However, this PT reads 7VAC on the filament leads. But like I say it worked in the Kustom. The circuit I'm using it in has 2 12AX7 tubes and using all heaters.

silverfox.

[RockinRocket]

Dang already ordered the power transformers the other day. Thanks for the help everyone. This will be my first attempt at a true bypass Boost pedal and was hoping to do DC heaters.

I am thinking of ordering this 3pdt http://www.mouser.com/ProductDetail/Car ... lkicLj8%3d .

That should let me true bypass and also switch on and off the indicator light correct?

This is what im building. I know the switching circuit isn't really worked out and the transformer diode sections alittle off. Had to use what I could find in the editor. The 1 m input jack is in the wrong spot and should be after the swicth before the grid stopper.
[IMG:836:749]http://i1225.photobucket.com/albums/ee383/superchampable/Boost-v2.png[/img]

[tictac]

It's weird but DC heaters do change the tone of an amp....

To my ears you lose a bit of sparkle or livelyness... it's hard to find the right word but after trying DC I've always stuck with AC heaters ever since and have never had noise problems.

As was mentioned you can tap off the B+ to derive a DC reference which works just as well but I've never seen a need for that either with proper layout.

I like the Dynaco trick of floating the heaters with a .02uF on the center tap of the heater winding. Cheap & easy....

TT

[Leo_Gnardo]

I like the Dynaco trick of floating the heaters with a .02uF on the center tap of the heater winding. Cheap & easy....

Seen that done in mid 60's Ampegs, floating filaments on a 0.1 uF 200V film cap. I've tried it in some difficult amps, sometimes that's the solution.

Just don't anybody do what a local first time builder did last week: 100K instead of 100 ohm filament balance R's. Oops. No biggie, his 5E3 just buzzed more than it should with volume controls up. Nice to find an easy cheap repair for once.

[SilverFox]

tictac wrote: It's weird but DC heaters do change the tone of an amp....

I think this would be an interesting topic to expound on. Not saying I don't believe it but, what would be the difference between an electron cloud created by a DC current v.s. an AC current? The sound, (noise), of water on an ocean shore v.s. the river bank?

silverfox.

[JazzGuitarGimp]

Looking at your schematic, you absolutely need a 1M grid leak resistor on the first stage, otherwise when the unit is bypassed, that grid will drift up and cause the triode to go into thermal runaway until it self destructs. Also, when using the third pole of your (amazingly expensive - check 3PDT on ebay...) switch for the led, wire the center contact to ground, then use the unused contact to ground the input of the circuit while in bypass mode. I reasize my second suggestion seems to nullify my first suggestion, but don't be tempted to build it without that grid leak resistor....

[Stevem]

Through the use of AX7s these days that have spiral wound filiments like some of the Sovtec's and whatnot I can not see a need to go thru the with all this DC powered stuff I gotta say!

[JazzGuitarGimp]

Looking at your schematic, you absolutely need a 1M grid leak resistor on the first stage, otherwise when the unit is bypassed, that grid will drift up and cause the triode to go into thermal runaway until it self destructs. Also, when using the third pole of your (amazingly expensive - check 3PDT on ebay...) switch for the led, wire the center contact to ground, then use the unused contact to ground the input of the circuit while in bypass mode. I reasize my second suggestion seems to nullify my first suggestion, but don't be tempted to build it without that grid leak resistor....

I just noticed R12 (1M) connected from the input jack sleeve to ground. This is the grid leak resistor I was talking about, but it's not wired correctly. Disconnect the top end of R12 from the sleeve, connect the sleeve directly to ground, and connect the top end of R12 to the left end of R1.

Also, both bridge rectifiers are incorrectly wired: the schematic shows the transformer secondaries (AC) connected to the DC outputs of the bridge rectifiers. This wiring will short out the transformer, and if not caught quickly, the transformer will overheat until it fails. The transformer secondaries should connect to the left and right points on the bridge and: on the upper bridge (HV) the plus output connection is at the bottom point of the bridge and the minus output is at the top point of the bridge; on the lower bridge (LED indicator), the plus output is the top point of the bridge and the minus output is at the bottom point of the bridge.

Also, notic that the only thing the DC output on the filament winding is used for is lighting the LED: the filament connections to the tube come durectly from the transformer winding (AC).

[RockinRocket]

Looking at your schematic, you absolutely need a 1M grid leak resistor on the first stage, otherwise when the unit is bypassed, that grid will drift up and cause the triode to go into thermal runaway until it self destructs. Also, when using the third pole of your (amazingly expensive - check 3PDT on ebay...) switch for the led, wire the center contact to ground, then use the unused contact to ground the input of the circuit while in bypass mode. I reasize my second suggestion seems to nullify my first suggestion, but don't be tempted to build it without that grid leak resistor....

I just noticed R12 (1M) connected from the input jack sleeve to ground. This is the grid leak resistor I was talking about, but it's not wired correctly. Disconnect the top end of R12 from the sleeve, connect the sleeve directly to ground, and connect the top end of R12 to the left end of R1.

Also, both bridge rectifiers are incorrectly wired: the schematic shows the transformer secondaries (AC) connected to the DC outputs of the bridge rectifiers. This wiring will short out the transformer, and if not caught quickly, the transformer will overheat until it fails. The transformer secondaries should connect to the left and right points on the bridge and: on the upper bridge (HV) the plus output connection is at the bottom point of the bridge and the minus output is at the top point of the bridge; on the lower bridge (LED indicator), the plus output is the top point of the bridge and the minus output is at the bottom point of the bridge.

Also, notic that the only thing the DC output on the filament winding is used for is lighting the LED: the filament connections to the tube come durectly from the transformer winding (AC).

Thanks for the input. Im aware of the 1m grid leak mix up as well as the transformers power section being off. Didnt really know that lingo very well but thought that could be close enough to get the point across.

The Light and heaters were lifted from the Soldano supercharger schematic. So whats the reason for DC on the light? Martin Manning mentiond the dc was used for "energizing the relay coil." For true bypass and a light will the transformer I bought be able to handle this if the dc is needed as shown on the Soldano schematic?

[martin manning]

A relay needs filtered DC but an LED does not. You can get by with just a current limiting resistor and a 1N4007 in series with the LED across the 6.3VAC, sized for 20 mA or so. That is very likely within the capability of the transformer. For a 2V red LED I'd go with a 220 to 330 ohm resistor.

[RockinRocket]

A relay needs filtered DC but an LED does not. You can get by with just a current limiting resistor and a 1N4007 in series with the LED across the 6.3VAC, sized for 20 mA or so. That is very likely within the capability of the transformer. For a 2V red LED I'd go with a 220 to 330 ohm resistor.

Im confused. A 3pdt footswitch is a relay that needs to be powered? Im realy new to pedals.

Would the Mesa boogie bottle rocket relay/light/true bypass schematic be something I should be cut and pasting for this project? And would work with my transformer?

[Stevem]

I have not done a A/B test in regards to a tonal shift/ change with tubes run on DC heaters, but I can see how that standing polarity in small 7 or 9 pin tube can effect the electron flow which then in turn must have some side effect!
I wish I still had acess to a spectrum analyzer , I would get that check out done right quick!