Suggestions for a 6L6 Cathode biased amp.

[ALBATROS1234]

As I posted recently on two different topics. I was building an amp in a 59' Magnavox record player upright record player console. Someone gave me this cabinet sans poweramp. Speaker comp is 15", 8" and 4" Magnavox speakers on a masonite baffle. At first, I was going to convert to two 12" period Alnicos but they won't quite fit. Last Friday I scavenged that Lowery organ which had 2 1958 Jensen P10Q's so I am thinking they are going in and of course I will cut a new plywood baffle. I was building a National 1224T but it just isn't coming out like I want. Therefore, new plan, 6L6 cathode biased amp and I would like suggestions. I was thinking a 5F4 tweed super but that one isn't cathode biased. The reason is I I need cathode bias is have a bunch of trannies but none have a bias tap. Can you build a cathode biased Fender tweed super? Any other suggestions on a 6L6 cathode biased amp that would sound great with 2- 58' Jenson P10Q's in a large deep record player cabinet?

[PRR]

There must be 69 amplifiers, or more, without a bias tap. Marshall rarely did.

[sluckey]

First off... you don't need a bias tap to build a fixed bias amp.

There are lots of Ampeg 6L6 cathode biased amps. Look in Hoffman's schematic library.

[dwinstonwood]

This is closely based on Hoffman's Plexi layout. I moved a few things around to suite my chassis.

The bias circuit comes directly off of one of the PT's secondaries, through the 220K/3W resistor, and then the diode.

[tubenit]

Can you build a cathode biased Fender tweed super?

Maybe something like this? 


With respect, Tubenit

[sluckey]

Here's a nice cathode biased 6L6 amp that began it's life as a jukebox...

     https://sluckeyamps.com/rocky/rocky.htm

[HotBluePlates]

... I scavenged that Lowery organ which had 2 1958 Jensen P10Q's ... Therefore, new plan, 6L6 cathode biased amp ...

Modern P10Q is rated for 40w but the originals would be more like 10-12 watts maybe.

Are you sure you want to risk blowing them with a 6L6 amp?

___________________________________________

If you do proceed with 6L6s, I would shoot for low B+ voltage.  Like a bit over 300v.

You don't need to make big power output, and low-voltage is likely to mean small-bias-voltage, which is going to make the power section a little easier to drive (so simpler preamp works well).

Stealing PRR's old suggestion, grab a handful of 100Ω resistors and stick maybe 5 in series between the shared 6L6 cathodes & ground.  Short-out a 100Ω to increase idle current, or place another 100Ω in-parallel with an existing 100Ω to trim the resistance down to 50Ω.  Odds are that you'll land mighty close to the usual 250Ω cathode resistor.

[tubeswell]

Supro Thunderbolt

[passaloutre]

I think all of my amps have cathode biased 6L6s. They sound great.

[ALBATROS1234]

The two suggestions I like the best from just reading this are Sluckey's jukebox amp and the Supro Thunderbolt. I was a bit concerned about the speakers even though to my knowledge I thought the fender tweed super used two P10Q's. I figured they would handle a cathode biased 6L6 amp fairly well. I do like the lower voltage suggestion as well. One problem I have had on a few occasions is when building a PS I end up having to increase the size of the resistors to drop enough voltage to make the preamp sound good. That is one spot I end up having to experiment and desolder depending on the PT because you kind of usually want 350 to 400 on the power tube plates, a wee bit less on the screens but then you want it to drop into the 100v range for the preamp tubes or else they are rip roaring and hit the power tubes too hard and you have no head room. I actually usually like the preamp tubes to have between 80 to 150v on the plates to get the tone I like which is a good edge of breakup with PAF classic rock tone. Thanks guys. I was scratching my head because there is so many schematics to go through and just looking at them when you haven't played through a particular amp doesn't tell you much. I do like Valco's, tweed Fender's and early amps in general but you can build a perfect clone of a head and if you don't have the identical speakers, cabinet dimensions and materials it will not be the same so it will always need tweeks to sound right.

Actually, maybe I should sell those 2 1958 P10Q's because they appear to go for $400 to $500 bucks each on Ebay and Reverb. I could theoretically buy 2 more reissue P10Q's which handle more power and still put cash in me pocket.