Search found 23 matches

by audiofanman
Wed Jun 02, 2021 12:34 am
Forum: Audio Bench & Dummy Load Setup, Test Equipment, Etc.
Topic: Variac input voltage?
Replies: 4
Views: 250

Re: Variac input voltage?

Mike, My take on this is the 110V version give you the ability to dial past 120. Useful when using load limiting (Not that a few volts less probably matters anyway) My setup is main house -> Vairac -> Isolation transformer than the load limiter if needed. When dialing the variac up, I watch the outp...
by audiofanman
Wed May 05, 2021 11:03 am
Forum: General Tube Audio Based Discussion
Topic: calculating true plate dissipation
Replies: 3
Views: 245

Re: calculating true plate dissipation

Regardless of PP, SE tube measurements, a lowly resistor the same method applies. I think some guy called Ohm as in Ohms law derived the relationship. We could convert the watts to BTU's by multiplying by something like 3.14 but that would be silly, not to mention piss folks off... So, current flow ...
by audiofanman
Tue Apr 20, 2021 11:08 pm
Forum: General Tube Audio Based Discussion
Topic: Calculating Bias Trim Pot/Resistor Value
Replies: 12
Views: 767

Re: Calculating Bias Trim Pot/Resistor Value

Hugo wrote: Tue Apr 20, 2021 8:25 am For the 6L6 and it is typically 11mA for a push pull configuration. That is in a range where you can no longer ignore it.
Understood! And 11mA showing up would be something i wouldn't want to disregard.. I guess it pays to know your valves!
by audiofanman
Tue Apr 20, 2021 12:59 am
Forum: General Tube Audio Based Discussion
Topic: Calculating Bias Trim Pot/Resistor Value
Replies: 12
Views: 767

Re: Calculating Bias Trim Pot/Resistor Value

Just to further my education, and from Marks videos... whatever current the plate sees, the cathode also see's, at least close enough to measure the cathode bias resistor and from its voltage drop, ohms law would get you to 99.9% of plate current. Again, from what I thought I learned, the grid doesn...
by audiofanman
Sun Apr 18, 2021 1:00 pm
Forum: General Tube Audio Based Discussion
Topic: 300B SE OPT 100% mystified !
Replies: 2
Views: 236

Re: 300B SE OPT 100% mystified !

Set up for the video, did a dry run and measured more believable numbers! I think I know what I did wrong yesterday. My lesson for today, if Im in doubt of the results, step back, take a second and run through all while making believe Im going to have Mark watching! Attached is a screen shot of my d...
by audiofanman
Sat Apr 17, 2021 11:14 pm
Forum: General Tube Audio Based Discussion
Topic: 300B SE OPT 100% mystified !
Replies: 2
Views: 236

300B SE OPT 100% mystified !

Poking around my amp, I figured I should try to figure out the OPT. I always hear folks say as far as big iron goes, its on the top of the list to upgrade if possible. Saw Marks excellent video a ton of times. Saw uncle Doug's as well, as many times as needed to really understand the deal. Between b...
by audiofanman
Mon Apr 12, 2021 11:46 am
Forum: General Tube Audio Based Discussion
Topic: Coupling cap replacement...
Replies: 5
Views: 431

Re: Coupling cap replacement...

Update... The schematic is not 100% correct. They have 2x 0.1uF caps and 2x 0.47uF caps in real life, while the schematic shows 4x 0.1uF... I managed to get the board out of the amp and trace the circuit, and see that they used a .47 uF coupling cap between the 12AT7 and the 300B. Im curious to lear...
by audiofanman
Wed Mar 31, 2021 10:02 am
Forum: General Tube Audio Based Discussion
Topic: Calculating Bias Trim Pot/Resistor Value
Replies: 12
Views: 767

Re: Calculating Bias Trim Pot/Resistor Value

Can you measure the voltage drop across the 33k resistor? Can you measure the 33k resistor? And, because I don't exactly understand whats happening there, is there only the one 33k ? If so, wont that one resistor show double the current as it's getting split by two tubes? I have a feeling the opt is...
by audiofanman
Wed Mar 31, 2021 1:06 am
Forum: General Tube Audio Based Discussion
Topic: Calculating Bias Trim Pot/Resistor Value
Replies: 12
Views: 767

Re: Calculating Bias Trim Pot/Resistor Value

So im such a newb at this stuff, i turn to ltspice for play time. Swapping component's cost zip, and cant waste stock i don't own lol. To verify my math i created a simple circuit and the dc voltage was the set to the measured voltage drop in my amps cathode bias resistor. The resistor in this simpl...
by audiofanman
Tue Mar 30, 2021 11:37 pm
Forum: General Tube Audio Based Discussion
Topic: Coupling cap replacement...
Replies: 5
Views: 431

Re: Coupling cap replacement...

Mark, The attachment option is complaining about file size.... Reducing it to the allowable size makes it hard to read... I created a folder in my google drive, an image and a marked up PDF is available Also an image of the insides (showing capacitor values and locations) The volume control board hi...