Weber Copper Caps and Bridge rec??

[67polara]

Has any one had any experience with these things and do they work well?  The Bridge rectifier is what I am interested in since I don't have a 5 volt supply.  Who do they work if anyone knows.

http://www.webervst.com/ccap.html

Tony

[FYL]

They work but aren't a good design IMO: many thermal problems and more than a few reliability/safety issues. Why don't you use some silicon diodes fitted with properly heatsinked series resistors? Cheaper, more effective and more reliable...

[tubenit]

I was shocked by one yrs ago and hit with around 476v when it (reportedly) put that voltage on the copper shell. It was explained to me that something that was supposed to insulate the voltage from that shell had failed.  I touched the copper when the amp was running to see how hot it was. Terrible experience for me.

I will never use another one. I have used ss rectification since then but inside the chassis. I am not saying others shouldn't use them. Nor am I saying they are all dangerous. Simply sharing what I experienced.

With respect, Tubenit

[67polara]

Can you show me how it is done?  I think I would get much more satisfaction if I build it myself, at least I learn something

Tony

[sluckey]

The Bridge rectifier is what I am interested in since I don't have a 5 volt supply.

None of those copper caps require a 5 volt supply. Your PT high voltage secondary dictates whether you need a bridge or not. If there's no center tap, you need a bridge. If you have a center tap, you should use one of the other (non-bridge) copper caps.

[67polara]

Sluckey thank you for that.  I understand, what I meant is that since I did not have a 5 volt supply I could not use a tube rectifier and thought this might be a way to get some of that MOJO without using one.  I do not want to add another transformer or change the one I have.  I already added an additional transformer for the filaments. Should have probably changed the transformer at that time instead but 20 20 hindsight is not helping me here.  I'll probably leave it as is just wondered what other people thought of this stuff.

Tony

[tubenit]

since I did not have a 5 volt supply I could not use a tube rectifier

There are several 6.3v rectifier tubes that don't use 5v.

You could use Hoffman ss plug in to an octal socket.

Look in his Library of Info and there are diagrams on building solid state rectifiers.

With respect, Tubenit

[kagliostro]

If I'm building something new and don't can use a tube rectifier I'll put on diodes as rectifier

mounted like in many amps, on turrets or eyelets

If I have an existing amp and want to use it with SS rectifier instead of the existing tube rectifier I can consider to build something with an octal socket and a copper "shield"

but I'll look to find some old mica sheet as to put in the inside of the copper tube as to prevent experiences as that tubenit ill-fatedly had

Kagliostro

[67polara]

OK, let me start over and give you more back ground on what I am doing.

I am modifying a Fender Blues Deville for Harp use for a friend.  He wants a tube rectifier but it will be to difficult to do because of the size and the transformer that is in it.  He wants that tube sag but it will be to difficult to do with what he has.  I was looking at the bridge rectifier with gz34 sag to try and get him what he wants.  I was asking the people here if they had any thoughts on it's use, if it works well and any problems with it, or is it all smoke and mirrors.  I have already changed the coupling caps and lowered the voltage on V1 and V2 to 95 volts.  I have rebiased  the power tubes.  I changed the v1 and v2 to 12Ay7's.  He is very happy with the way it works and all but still wants to hear more sag.  Only things left to do is tube rectifier and Paraphaze inverter and tweak the tone circuit and he ends up with a bassman that I told him to buy in first place LOL.

Sorry I didn't explain it better from the start.  I just figured someone would jump in and say works good, crappy or not worth the time for the results.

Tony

[FYL]

Then it's pretty easy: just add a series resistor between the bridge and C34+C35. A 47R to 100R / 25W resistor should be OK. The resistor will get quite hot and carry B+, so it should be suitably heatsinked and fully isolated.

[67polara]

Thank you FYI.  So this will create the Sag he is looking for?

Tony

[phsyconoodler]

Yes it causes power supply sag.However,I would use a 120 ohm resistor.More sag.

[PRR]

.

[67polara]

Thanks to all that is way easier and cheaper to do. 

Tony

[bluesbear]

I've done the diode/resistor thing and it works great. I recommend a 50 watt resistor, though. I put a fan in mine because it REALLY gets hot and I had a small and confined space to deal with.Bottom line, though, is that it works.
Dave

[kagliostro]

As to increase sag

(when you want)

there is also the way adding a resistors in series with the resistor connected to the grid of the power tubes

then put in parallel with this resistor a switch

so if switch is closed the resistor of the grid is the standard resistor

if the switch is open the grid resistor value increases increasing sag

as an example

if the standard grid resistor is 470R and the added in series resistor is 2.7Kohm

(having a switch in parallel with the 2.7Kohm resistor)

if the switch is closed give the standard 470R

if the switch is open give 470R + 2.7Kohm increasing sag

this is done in some Mesa Boogie, don't remember the model

Kagliostro

[tommytornado]

You know.. considering this is for harp and he wants more sag..  I'd more than double the size of the sag resistor (250-330 ohms).  As others have said, it's going to get really hot if the wattage value is too low, so be very careful.  Also, if you've pulled the PCB, I would suggest pulling the in-rush current limiter thermistor off the old board and put it right after the sag resistor.. before the 1st filter cap.  This will save some wear and tear on the power tubes. 

Also.. more sag.  If this is a 4X10" blues deville.  The best thing you can do for it is some alnico speakers (if you haven't done this already).  Two Signature Series alnico 10"s on top will really sweeten up the harp tone and let him hear more sag.  (it'll help with feedback as well)

FWIW, the Weber Copper cap contains diodes, 2 wire wound resistors and a thermistor mounted on a PCB.. connected up to an 8 pin tube socket enclosed in a closed end copper tube.  They also sell them in little metal boxes that can be mounted inside an amp chassis.  While I like the concept, would still suggest rolling your own (rectifier) if you have the knowledge and ability to do so. 

[HotBluePlates]

As to increase sag

(when you want)

there is also the way adding a resistors in series with the resistor connected to the grid of the power tubes

...

if the standard grid resistor is 470R and the added in series resistor is 2.7Kohm

(having a switch in parallel with the 2.7Kohm resistor)

if the switch is closed give the standard 470R

if the switch is open give 470R + 2.7Kohm increasing sag

this is done in some Mesa Boogie, don't remember the model

Kagliostro

This is referring to the screen grid (pin 4) of the output tubes.

I didn't realize Mesa had done this in some amps. It is a trick I have suggested for quite a while to create a sag effect. It works regardless of the operating class of the output stage; a big series resistor in the power supply might not give a sag effect in a class A amp without severe voltage drop. This trick works because screen current varies from idle to full power, and reduced screen voltage limits plate current. A "too-big" resistor in series with the screen can can voltage drop as the tube starts approaching maximum power, and can dynamically limit plate current and output power. In other words, give sag.

The value of the resistor is best found by taste test. Start with 2.7-3k and adjust up or down based on the whether you get the desired sag at the desired maximum volume. Going too high can restrict the actual maximum output of the amp, and that makes the option to switch back to 470 ohms a good idea. Do all switching with the amp off.

[tommytornado]

.. yea, that's the ticket...  The big screen grid resistor is the way to do it even better and way easier/cleaner/without generating all that heat. 

[kagliostro]

Hi HBP  

If I know which is the purpose of that resistors is because you explained it to me some time ago

and ... yes, Mesa do it in the Lonestar, see link below

http://www.schematicx.com/view-schematic/mesa-boogie-lonestar-schematic/

click <Download Schematic> in the left part at the middle of the page

under:

Filetype: PDF  |  Filesize: 1,207 KB  |  Updated on June 16, 2010
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Filename: mesa-boogie-lonestar-schematic.pdf
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Download Schematic

p.s.: don't confuse the lonestar arrangement with those present in the Mark IV

http://www.freeinfosociety.com/electronics/schemview.php?id=287

Kagliostro