Blues Master Questions, etc.

[didit]

Also, where is everyone able to find the 300uf caps?

Today one is best using a quad of 150uF 350-400V rated radials a la Dumble's quite flexible precision power supply design. I find several available & suitable components for US$4 and up searching Mouser just now. For example search for 647-UCP2G151MHD6.

Best .. Ian

[JD0x0]

are you guys running your low plate classics with a 12AY7 PI like the original 2nd gen amps ?

That makes a difference to the volume/gain hitting the output section as it's lower gain than a 12AX7.


I put a 12AX7 in mine originally as I thought louder was always better but after talking to Tony he suggested I go back and give the AY7 a chance and I've stuck with it.


M

Dont you mean the 12AT7? That's what I have in my 2nd gen.

I run AT7's in the PI of most of my amps now-a-days. The AT7 drives more current and has a lower output impedance (which reduces chances of blocking distortion on the output tubes).

Also, FWIW, according to the Ampbooks calculator, even though an AT7 has a lower gain factor than a 12AX7, it appears in a LTPI they have nearly the same gain (it actually shows the AT7 with slightly more gain)

Try the two tubes with the same plate load resistors, the gain is virtually the same.
https://www.ampbooks.com/mobile/amplifi ... iled-pair/

[norburybrook]

Interesting thanks for that. You can hear a difference though if I swap out the AT7 for an AX7 in my 2nd gen ODS. Obviously our ears always think louder is better when comparing so that's what I went with but Tony A said to go back and put the AT7 back in and live with it for a while . That was good advice as I learned to love the amp like this. It's different it needs to be loud to work but it's a great amp.

M

[jwhousley]

are you guys running your low plate classics with a 12AY7 PI like the original 2nd gen amps ?

That makes a difference to the volume/gain hitting the output section as it's lower gain than a 12AX7.


I put a 12AX7 in mine originally as I thought louder was always better but after talking to Tony he suggested I go back and give the AY7 a chance and I've stuck with it.


M

Dont you mean the 12AT7? That's what I have in my 2nd gen.

I run AT7's in the PI of most of my amps now-a-days. The AT7 drives more current and has a lower output impedance (which reduces chances of blocking distortion on the output tubes).

Also, FWIW, according to the Ampbooks calculator, even though an AT7 has a lower gain factor than a 12AX7, it appears in a LTPI they have nearly the same gain (it actually shows the AT7 with slightly more gain)

Try the two tubes with the same plate load resistors, the gain is virtually the same.
https://www.ampbooks.com/mobile/amplifi ... iled-pair/

I have tested a 5751 in different circuits for the PI as well...

[talbany]

Technically speaking the 12at7 is a far superior tube for driver applications. The wimpy (by comparison) 12ax7 should be used strictly for voltage gain applications IMO, and the requirements for the driver are often current/slew rate/low impedance related. The 12at7 has plenty of gain (70%), a higher plate dissipation rating, and a much lower output impedance and will handle much higher voltages. In short, it is a better driver tube, especially if its increased max ratings (compared to the 12ax7) are taken advantage of. This will translate primarily into better HF response and transient recovery and an overall punchier output section

On the other hand, it's common for great-sounding guitar amps to violate general rules about what is "technically" best. Given the overall circuits,

Tony

[jwhousley]

Maybe one of these would be useful as a starting place? I strongly encourage you to have a schematic that is an EXACT match to what you're wanting to do along with a layout to
go with it prior to ordering parts. There are some editable SCH files of different Dumble amps. And there are schematics and layouts in the file section under each amp such as 102,124, and 183.

https://tubeamparchive.com/viewtopic.php?f=5&t=5719

https://tubeamparchive.com/viewtopic.php?f=5&t=17449

With respect, 10thtx

Thank you!

One thing I noticed the "Xicon Carbon Film 1W 5% 10k tone stack bass" doesn't match the layout or schematic I have. It has this as being a 1.8k, not 10k for the bass tone stack R value??

Scratch that... I must of had an older layout and schematic store... oops...