Added Tube Rectifier - Bandmaster

[lowell]

I added a 5v transformer and installed a 5y3 tube rectifier in one of the available power tube sockets of this Blackface Bandmaster. I am running the primaries of the 5v transformer from the same points as the PT... in order to utilize the mains fuse for both transformers. This tube is rated for 2amps for heater... wow, I'm thinking I should up the mains fuse from 2amps to 4 or 5. What yall think? Or maybe I should added a separate fuse for this 5v transformer?

[TD_Madden]

You're only running ONE power tube?

[lowell]

No this amp has 4 power tube chassis holes and only 2 are utilized being that it's a 2 6l6 power amp. I stuck the rect in an empty hole... ha! funny question.

[lowell]

PI conversion in Bandmaster

I'm also curious what I can do to the PI to make this amp more Tweed'ish. I've converted this amp to half of a cathodyne PI per the 5E3 but to my surprise the amp is cleaner, not dirtier with this mod. What I mean by half is that I left the gain stage before the cathodyne out. My reasoning for this is that this amp already has a tone stack recovery/gain stage and that this would be too much gain. Is this wrong? Shall I leave that extra pre-PI gain stage in for the cathodyne to work correctly?

[Bruce / Mission Amps]

I added a 5v transformer and installed a 5y3 tube rectifier in one of the available power tube sockets of this Blackface Bandmaster. I am running the primaries of the 5v transformer from the same points as the PT... in order to utilize the mains fuse for both transformers. This tube is rated for 2amps for heater... wow, I'm thinking I should up the mains fuse from 2amps to 4 or 5. What yall think? Or maybe I should added a separate fuse for this 5v transformer?

No... 5v times 2a = 10 watts.
Your fuse is handling 10 more watts of total power through the power cord.
I'd use a 2.5a to 3a slo-blo fuse and that would be all.

[Enzo]

What Bruce said. The extra 2 amps is not coming from the wall, it is coming from the transformer secondary.

[lowell]

oh yeah... duh, thanks guys.

[lowell]

I'm also curious what I can do to the PI to make this amp more Tweed'ish. I've converted this amp to half of a cathodyne PI per the 5E3 but to my surprise the amp is cleaner, not dirtier with this mod. What I mean by half is that I left the gain stage before the cathodyne out. My reasoning for this is that this amp already has a tone stack recovery/gain stage and that this would be too much gain. Is this wrong? Shall I leave that extra pre-PI gain stage in for the cathodyne to work correctly?

any ideas on this?

[txstrat]

Most of the "tweed" sound is made up in the preamp due to tone stack and caps values. The cathodyne PI should be liable for more grain anyhow.
You can add more tweedish sound to your bandmaster tone stack by adding a .0027 cap parallel to the 250pF cap on the treble pot (look at the champ II schematic: http://www.schematicheaven.com/fenderamps/champ_II.pdf ).
The triode before the cathodyne in the 5e3 is the recovery of the tone stack - no need to add it, unless you want way more gain

[TD_Madden]

No this amp has 4 power tube chassis holes and only 2 are utilized being that it's a 2 6l6 power amp. I stuck the rect in an empty hole... ha! funny question.

Ok, I didn't realize you had added a socket to one of the unused (covered) holes.

[tubeswell]

any ideas on this?

+ what txstrat said. The stage before the inverter in the 5E3 is the driver stage for the inverter (since the inverter by itself only has 'unity' gain). So if you haven't got a driver stage pumping the volts into the inverter grid, you won't get much out of the inverter. But it also depends on what output tubes you are running. Bigger output tubes need more juice on their grids. The 5E3 is 'only' running 6V6s, which don't need as much juice (to make them clip) as 6L6s do.

[lowell]

ok so I modded the preamp dropping resistor to get 5E3X2 voltages i.e. 170v on preamp plates and 260v on PI plates. So I now have those voltages, tube rectifier (5Y3) engaged with 380v on power tube plates and cathode bias running at 55ma per 5881wxt. My preamps are all 100k load with 820/25uf cathode combo in first stage and 1.5k/25uf on tone recovery stage. This setup with the cathodyne PI STILL will not sound anything like the 5E3 whatsoever. The only difference I see at this point is the tone stack, 5881 instead of 6V6 and the transformers.

The amp is no where near as dirty sounding as a 5E3, and the tone is I'd say maybe 50% there. I'm wondering why all these mods have not produced adequate results. Sure the transformers are different, maybe the OT is more heavy duty than a 5E3 causing cleaner louder tones with tighter bass, and the 5881 tubes could be having a similar effect. If I'm right with this then this is a great lesson on what affects the tone of an amp and how MUCH it affects the overall sound. This proves that the output transformer, output tubes, and tone stack are VERY much part of an amps sound. I could have assumed that certain stages and components of an amp have a certain affect on the sound, but this is a great hands-on testament to it. Out of curiosity and lack of time to go further with these mods could someone tell me if they think the missing link here is the 6V6 tubes? Or OT? Or tone stack? I'm guessing someone will chime in and say all 3, but of the 3 what would be changed first? Oh wait just remembered, this amp has a choke! I will try replacing that choke with a good 'ol resistor... I forgot 'bout that.

[txstrat]

I'd say most difference makes the tone stack followed by the OT in combination with the tubes. As you said the heftier OT will be cleaner at same volume level and the tubes will too (imagine a 5e3 OT with 6V6 or -properly biased 6L6 - the sound difference is not THAT big).
Also the choke will not be a big difference in overall sound - more like different behavior of the amp. There are some threads in this forum where this is the topic. -> search
Your voltages are OK IMHO so I'd expect your amp sounding "tweed" with the different tone stack, although (due to the OT) might not be as dirty.

[lowell]

txstrat thanks for your input. Yeah I'm thinking 6V6 might add some of that earlier breakup per the tweed sound too. I'll keep all that in mind for future mods.

[mac1amps]

A Bandmaster is a 40 Watt amp. You should be using a 5AR4/ GZ34 rectifier. 5Y3's are used w/ 15-20 Watt amps.