The Amp Garage

load line is tangent to the 100% Pa max curve ? Help me see that. You're going to have a hard time seeing that because the JJ curve is actually for 12W instead of the 14W label. With 450V and 12W, R comes out to 16.875k so that 4.219k would be used for the class B load line. The line will run from ...

Here is a straightened-out Concert Series schematic. There isn't really a Concert II, but everybody uses that designation because all of the other ones are "II's".

... but what the hell are those boxes with the little plus sign? Those are VTL5C1 light dependent resistors (LDR). They have an LED and a photocell inside them. When the light from the LED hits the photocell, the resistance of the photocell plummets. VTL5C1-5C4 PerkinElmer.pdf Fender Deluxe Reverb ...

Hello, I'm in the planning stage of building an amp with the foundation being the 5F6-A. I've got a great power transformer that I'm going to use, however it doesn't have a bias supply tap. I have Merlin's book on both preamps and power supplies, but I'm still struggling to understand the precise s...

The bias is connected to the oscilator circuit. Just trying to understand what is happening here and why. Sometimes the neon lamp in the LDR unit will remain lit when the LFO stops unless you put the LDR driver tube into cut-off. If the neon lamp remains lit, the Intensity control acts like a volum...

So I built the thing and got an open loop gain of 1.824 with no regard for significant figures. Using this in the closed loop equation above, I calculated a closed loop gain of 1.766. The observed closed loop gain was 1.774, pretty close. The observed gain reduction was 1.774/1.824 = 0.973 = 0.24dB....

I'm not really following much of that, so I took off in my own direction. The cathodyne already has 50% NFB, 30.2dB of gain reduction, before the 3.3M local NFB thing. CF 11 PNG.png So I used the gain without the 3.3M local NFB as the open loop gain. I used this cheat sheet for the closed loop gain....

For the TD I'm also interested in the differential gain because I am only trying to find the equivalent input resistance, Rin. So, by taking the resistances of the plate and tail and balancing them, rendering them equal, I have a "close enough" factor I can use in the object of the exercise, which ...

Before we can determine the bootstrapped value of Rg and hence the effective input resistance ( Rin ) using the bootstrap formula below we need to find the value of the differential gain ( A ) PI equations (1) bootstrap formula.jpg The formula for differential gain takes the 'total output voltage, ...

Kee22 wrote: ↑Sun Mar 10, 2024 4:06 pm Its not a 5f6a that's my conclusion but probably based on it. The cap i actually correct because of the original board layout. This is the front and back.

The picture of the bottom is incomplete.

xtian wrote: ↑Thu Mar 07, 2024 9:37 pm That 50p value is on both the layout and the schematic, from the Dumble Files section...

Ah, I see. Probably been discussed to death, eh? Thanks.

I had a chance to swap in an LND150 in place of 12AX7 first gain stage with no other mods in an existing build, and was happy with the results. So I'm going ahead with this Liverpool (nontraditional!) build, using LND150 as first gain stage, thereby eliminating one preamp tube. Layout first. First ...

I guess I'd have to see your math. I used a mu of 100 and an internal anode impedance of 62.5k for the 12AX7. I used a mu of 17 and an internal anode impedance of 7.7k for the 12AU7. The external cathode resistance is 2.2k in parallel with the 10k pot for a total of 1.8k. The 1M grid leak resistor ...

TUBEDUDE wrote: ↑Tue Feb 27, 2024 12:11 pm This loop uses a cathode follower topology doesn’t it?

I believe it looks something like this:

It's not about the gain per se. The 12DW7 optimizes the driver and recovery functions. The AX side provides high gain for the recovery signal. The AU side provides a low impedance output capable of driving the cable without high frequency loss due to cable capacitance. You might want to check my ma...