Standel 25L15-Do you like it as is or would you like to change something

[wsscott]

I'm working on the bias circuit in this cathode biased amp, and the schematic gives the option of making the cathode bias resistor adjustable using a 100 ohm pot plus a resistor vs. just a single value resistor.

This option calls for a 100 ohm pot plus a 68 ohm 2 Watt resistor.  I failed to order the 68 ohm 2 watt resistor, I just have 1/2 watts on hand.  But I do have a 100 ohm 2 watt resistor.  Would substituting this resistor create issues in adjusting the bias--or otherwise?

Thanks.

[sluckey]

Kinda hard to answer without access to a schematic.

[shooter]

But I do have a 100 ohm 2 watt resistor. 

more R = less I (I= E/R)
so you are "safer"
start WITHOUT the adjustability, get the basics dialed in, then tinker...so install the 100, figure out what the tubes are dissipating, figure out if they go into cut-off, figure out how it sounds......


then tinker

[wsscott]

Thanks Shooter-I figured there might be a math analysis involved that only some people would know.  Certainly not me!

[shooter]

 


it's not "math", it's the language of electronics 

[wsscott]

Does anyone know how the new Standel amps back light their front panels? I think Magnatone also has some models that are backlighted. They look really cool, and I'd like to try it some time.

[kagliostro]

HBP did it on his Standel

The light is placed around the panel

Go here
 
https://el34world.com/Forum/index.php?topic=13326.msg129564#msg129564

And read the post from Doug

Franco

[wsscott]

Thanks!

[wsscott]

I've almost completed building the Power Amp section, and wondered if there is a way to test it. This section is where the AC comes in and contains the PT, OT, 2 chokes, and the rectifier and 2 6L6's.  The on/off switch is in the preamp, not this section. Since I haven't started construction of the Preamp, I don't have a way to inject a signal, or anything else, but I want to make sure this section of the amp is wired properly.

[sluckey]

How can you continue to ask for help on this project when you won't share the schematic? I understand honoring someone's request to keep the secret, but if everyone honored that secret then you wouldn't have the schematic. Think about it!

[shooter]

wondered if there is a way to test it.

sure, no problem, just provide the following;


total expected;
 filament current/voltage
 preamp current/voltage
 PA current/voltage

then you can calculate a dummyload for testing

[wsscott]

Thanks Shooter.

[wsscott]

Assume the attached Gretsch schematic of the 6165's power amp has the AC power line and fuse attached at the PT's primary windings.  Other than that, no controls and nothing from the Preamp is connected.

[kagliostro]

To test if it works you can use the preamp of one other amp or a signal generator or arrange a partition resistor from the output of a small transistor radio

Franco