The Amp Garage

A significant part of what I associate with the circa 1968 100w amps is the very relaxed filtering, especially by comparison to the amps from 1969 and later (I'm thinking specifically of later amps with serial numbers with the prefix SL/A; these amps generally reflect what's shown on the Unicord sch...

Ceriatone has layout for their version of the circuit that's very similar to the schematic on the Mark Huss site:

Sounds to me like it may be an ergonomic issue related to usability of the lower registers of the volume controls than an electrical issue related to the overall gain structure. Have you tried more aggressively tapered volume pots? If you're using the common 30% taper, 15% or 10% may be easier to di...

Because of the impedance issues that come with any L-pad setup, I'm not convinced it's possible to present a consistent reactive load to an output transformer while maintaining continuously variable volume control as opposed to stepped settings (e.g., as with the JohnH attenuator). However, a dummy ...

Seems to be back working! The other hosts were working fine, so it seems like the url's catalogued on Google were associated with the one host that had a hiccup. I do love having those datasheets available, especially from different times and manufacturers, so I'd love to see that, Colossal!

Hopefully this is a silly mistake on my end, but has anyone been having difficulty with frank.pocnet.net lately? Generally when I look for a tube datasheet I can find the one I'm looking for by Googling the tube type and something from that site returns as the first or second result. However, lately...

If the amp is working right now with those idle measurements, I think it'd probably be fine to just check how much your screens node sags with a strong input signal. To hit that 412V value Martin described in his earlier post, the screens node would have to sag about 90V, which would be on the very ...

Sounds great for a test rig! If someone wants to try this in an actual amp, it may be a good idea to isolate the first node from the power supply via a choke or a resistor between the need for filtering out the high-frequency hash and the absence of any kind of sag given that it's regulated.

Have you tried pulling tubes with the amp running to isolate the fault? If you start in the order of the signal chain, you might be able to rule out the earlier stages of the amp. I am noticing that overall the MK1 seems to drive the PI harder, so I'm wondering what happens if you disconnect the NFB...

cdemike - you hit closest to what I'm trying to do - hoping that a lower efficiency rectifier tube will take care of a lot of the voltage drop and get it close to the plate voltage that the OG amp was designed with. I was even considering a 5y3, but I think that I saw this voltage is too much for i...

This is the paired cathode follower suggestion I was describing. The input would need to be after some kind of resistive mixer.

This could be a really cool project! Kind of makes me think of a Bassman or early Marshall in terms of the gain structure. I definitely think this is possible, though your preferences in terms of coupling the cathode follower will dictate how difficult this might be to implement. If you're looking j...

Nuke beat me to getting a response written out, but in case it's helpful to understand the math, I've included that below. Long story short, though, I agree with nuke and don't think that calculator is accurate for what you'd expect from a 5U4-rectified power supply. You could probably expect to get...

If your concern is handling DC on a standby switch, you could always have a double pole standby switch that (dis)connects both of the HT taps from the B+ rectifier. If your power supply uses a center tapped PT, then the bias supply can then draw from one pole of the standby switch. Obviously if you'...

I understand having the "first draft" of an amp be an all-access type of build that eventually gets simplified with time. I built a 4-hole Marshall circuit that way and eventually settled on something similar to a Bass-spec amp. I think I'm reading that your goal is similar. If that's the case, then...