The Amp Garage

Tony Bones wrote: ↑Thu Jun 13, 2019 7:10 pm Be aware that the metal case is connected to pin 1, so it's not safe to use that pin as a tie point for grid or screen resistors.

The case pin can be used for an earth connection to shield the tube.

pdf64's post has a link to an IOS app called Tonestack Kit, which works on iPhones. It has the top boost calculator as well as AB763 and others, so you can compare circuits and plots

Liability Insurance is there to protect* you against being sued for negligence by a victim's lawyer if they die of electrocution using your amp. It doesn't deal with professional registration, which you need in order to even get liability insurance. * Up to a certain price point - whatever the insur...

Which brings me to the billion dollar question , is a parallel loop simply a series loop where the signal is being split where the bypass switch usually is? As in, 50% of the signal goes to the send jack and 50% past the loop? Parallel loop keeps a permanent ‘dry’ signal pathway, which the FX loop ...

Have you considered the possibility that one of the filter cap ground returns is not connected due to a dead trace? (which could be causing the filter cap at that node to lose its decoupling function? Check the DC voltages on the HT supply rail to make sure that they are not all the same throughout ...

We have Katipo spiders in the dunes nearby. http://www.marinelife.ac.nz/species/5342/Katipo%201%20%20RM.jpg We also get Redbacks. https://www.abc.net.au/news/image/1155548-3x2-700x467.jpg And they can interbreed, producing a more deadly hybrid These are the same genus, Latrodectus, of which there ar...

^what xtian said^

The 5VAC coming off the rectifier winding would otherwise present as 'varying DC' riding on top of the rectified B+, but for the fact that it is smoothed out by the filter cap (along with the much bigger rectified 'pulses of DC' from the High Tension supply).

... So you recommend 20k for plate and tail R on the cathodyne instead of 47k? Not me. The datasheets. Its a higher-current tube than a 12AX7. More current = more voltage across a given resistance, so with a higher current tube, you don't actually need 47k load resistors to get a decent voltage dro...

FWIW The ECF82 triode is more like a cross between a 12AU7 and a 12AY7. highish transconductance (8.5mS), low plate resistance (5k) and u=40. Recommends a 20k plate resistor here https://frank.pocnet.net/sheets/129/6/6U8.pdf Tried a 6U8 in front of a 20W amp a few years back. See schematic. I don't ...

...Frequency doubling would be my guess. The 'dip' in the lower sine wave peak mirrors the negative peak of the upper sine wave. This is probably due to the hot bias of the LTP, which would increase the onset of grid current limiting. Merlin discusses this on p172-173 of the 2nd edition pre-amps bo...

Master volume at 1 (bedroom volume). The bottom trace shows the weird distortion that confused me a lot. https://live.staticflickr.com/65535/32806086177_fe6de939ce_b.jpg Frequency doubling would be my guess. The 'dip' in the lower sine wave peak mirrors the negative peak of the upper sine wave. Thi...

Yes, the Pr:Sec winding ratio is halved, and for reasons I explained earlier, the load to the ‘on’ tube is halved ( because only 1 tube is delivering AC- through half of the primary winding). So it’s the same as running a tube ‘1-knotch’ away from the optimal load. Output power will be reduced. The...

Yes, the Pr:Sec winding ratio is halved, and for reasons I explained earlier, the load to the ‘on’ tube is halved ( because only 1 tube is delivering AC- through half of the primary winding). So it’s the same as running a tube ‘1-knotch’ away from the optimal load. Output power will be reduced. The ...

Silly me, I was thinking ‘put the signal to ground’, and I said ‘Ground the grid’, which of course would be bad in fixed bias. Happens when I’m in a rush. 🏃🏼‍♂️ Killing the signal on one side of the power amp means that output tube isn’t effectively conducting AC, so the OT primary on that side will...

Sure - lots of guys here have done that. Ground one of the output tube grids - either with a switch or a pot. The 'off' tube will not be conducting, so the Pr:Sec winding ratio 'seen' through the OT halves (which changes the impedance ratio - lowering the reactive load to 1/4 of what the plate-to-pl...