The Amp Garage

Stevem wrote: ↑Mon Apr 28, 2025 3:39 pm I don't know about the early 77 100 watt twin stuff because I have 76 master volume 70 watt PR and its my understanding that Fender started both models off with UL at the same time.

Let's see it.

Here are 45W Pro Reverb transformers with '77 date codes.

Stevem wrote: ↑Sun Apr 27, 2025 6:50 pm A 77 twin would have been the 135 watt model and had a UL output transformer so it would have had two more primary leads.

Not that it's relevant to the current thread, but Fender made 100W Twins for the first part of 1977 and then made 135W Twins for the later part of 1977.

The OT and PT are likely from the eighties. The 21009 OT was used on the Twin Reverb II.

solderhead wrote: ↑Tue Jan 21, 2025 5:23 pm ...garbage-in, you should expect to get garbage-out.

I believe that Dr. Emmett Lathrop Brown proved that one to be a total fallacy.

R.G. wrote: ↑Sun Jan 19, 2025 4:19 pm For a multi-tapped output, the primary impedance is as stated ONLY when one and only one resistor of the designed output impedance loads the secondary.

What if you loaded the eight Ohm tap with a sixteen Ohm load while also loading the four Ohm tap with an eight Ohm load?

Langmuir was paid by the U.S. government to pose as a debunker of UFO's amongst other things. He was not a debunker in the strict sense of the word because debunkers take things that are false or at least distorted and exposes them as such. Langmuir took things that were true and tried to convince u...

kev02 wrote: ↑Fri Aug 23, 2024 4:55 pm Can anyone pont me in the right direction for thru hole ferrel ? I have no luck on the web yet .

Are you talking about ferrite beads?

I am laying out an amp with a DC coupled cathode follower where it would make more sense to use two separate tubes instead of both in the same envelope. I can't think of a reason why having the gain stage in a separate bottle from the follower stage would be a problem, but I don't know if I have ev...

mhuss wrote: ↑Wed Jul 17, 2024 9:15 pm I've been running a 'matched set' of JJ KT88s in mine without issues.

Thanks for the tip.

So its actually one step 'worse' than a normal half-wave rectifier circuit. They make up for this by using massive "soup can" 450 or 650uF stacked filter caps and a sturdy filter choke before the output tube screens and downstream. I wonder how it is worse than a half-wave rectified circuit. The vo...

mhuss wrote: ↑Tue Jul 16, 2024 8:25 pm The 400 PS (and 300 PS, I actually own one of these - anyone want to buy one, lol?)

No thanks, I already have one of each. I bought the 300PS new when they first came out. After the second set of overly expensive 6550's blew along with all the collateral damage, I shelved the thing.

YOu are correct it was an AB568 but turned into an AB763 Bias is adjustable. SO tha's a 1 ohm and I can read the value right there ? IF I try to measure that resistor Iget an unusable reading keeps jumping up and down... and where do I measure screan curent ? Thanks ! Yeah, read the voltage across ...

THe death cap is there but nt cnected to anything. a 3 prong cable is installed. So, what is that blue resistor for ? And what is going to what seems to be pin 6 wich is unused in that tube ??? Let me see if I am getting this. Bias supply is coming in on pin 5 trough the 1.5K resistor across pin 1 ...

Mark wrote: ↑Mon Jun 24, 2024 1:37 am I’m running the amp into a 4 ohm load.

Did you ever say what kind of 4 ohm load?

The SF Twin is putting out 55vpp on both sides of the P.I. stage. I will check what is on the plates of the output valves. There is 46vpp on the secondary of the output transformer. I’m running the amp into a 4 ohm load. The AC voltage on the output valve plates would be good to know. What kind of ...