Choke for a 5150

[Enzo]

Now that the amp is stair-ready, you can learn Stairwell to Heaven.

Lemme ask you this, do you crank the beJesus out of the amp? I mean all out 110%? Because really, most of the tone of this amp is in the preamp, and unless you totally slam the thing, the power tubes won;t be overdriven. What do you plan the KT88s to accomplish?

[JacksonRR]

Well I bought a quad of Shuguang Golden Treasures. Two are in the outsides of my 333XL. The change from EL34 was insane. I do play loudly. I'm not looking to overdrive the power section, that's one plus for KT88. The tight but large bass response, plus numbah 2. I just overall like the sound of them. They are more detailed and hi-fi than any other power tube I've ever tried. I have driven the 333XL into power amp distortion on a number of times. When a KT88 distorts it's a beautiful thing, totally unlike EL34 or 6L6.

So what's the verdict? Two on the outside getting a thumbs up for functionality?

[Steve Conner]

KT88s should be OK in the Bugera if it had EL34s from the factory, and you rebias it. If you just swap in the KT88s with the bias still set for EL34s, they'll draw excessive current.

In the 5150, you have to be careful because KT88s draw more heater current than 6L6s and could overheat the PT. KT88s and EL34s are rated at 1.6 amp heater current, 6L6s at 0.9.

Installing only two KT88s would be a reasonable way to mitigate that. But do you mean two KT88s on the outside and no tubes in the other two sockets? or two KT88s and two 6L6s? or two KT88s and two EL34s?

Also, KT88s have wider bottles than EL34s or 6L6s, so might not fit. I've heard of a few people trying to move the tube sockets in a 5150 further apart to accommodate KT88s, and they ended up bodging it and wrecking the amp completely. Yes, worse than throwing it down the Stairwell To Hell.

I used to run EL34s in my hi-fi, but I changed it to KT88s. I swear that they sound different even at low volumes. They seem clearer with less distortion.

[Enzo]

WAIT!!!

Seems to me.... Is pin 1 on the KT88 wired to the metal base ring? That is the case on some odd tube or other. Or is it a separate suppressor grid as in the EL34? Or is it 6L6 wiring?

Pin 1 is not wired on the end socket in the 5150.


And be very careful, in some Peavey amps, they took advantage of the non-connection of pin 1, and ran the trace to pin 3 right square across pin 1 to get to 3. On the 6L6 the amps were designed for, that is no problem, but stick an EL34 in that socket and you get B+ on the suppressor grid. And on any tube with pin 1 wired to shield or the metal base ring, and there is B+ on that metal base. You really must check for that sort of thing first.

[JerryP]

Wait. It just clicked. If I use the 1M pot instead, am I installing the FJA mod that costs $145?

The mod I do is more than just adding diodes and a pot. It is similar to the circuit Peavey uses and like the other guys have stated, that circuit will work in your amp. My mod turns the noise reduction off when using the rhythm channel.
The price of a mod is based on way more than just the parts and labor involved. I also spend time, sometimes hours on the phone and email with customers, un-pack and inspect amps, deal with shippers if there is a problem, re-pack and ship amps. I usually have 2 hours of my time into each amp before I ever touch it when all is said and done. If I goof I also cover shipping to get the amps back so these all go into the cost of me doing business which has to be paid for. Add to that the hours I spend talking with people who don't send work in and helping folks online. I get paid nothing for that.
Jerry

[JacksonRR]

Can't tell. They're all black inside. Special coating of Sars or something. I'm sure they can't be wired any differently and they'll be as cool as the two in the integrated quad Steve is referring to. Yeah, I just wanna do two on the outsides because they don't fit inside and the integrated quad is stupid.

Hey Jerry, I really didn't mean to ruffle your feathers. It's not about what you're doing, it's about what I'm doing. You ,as the king of 5150 mods, are the reference point. Your pdf on the bias mod is still floating around. Thankyou.

[Enzo]

You're sure, but I'm not, for instance, you can't just plug EL34s into the 5150.

Never mind, I looked it up. The suppressor is wired internally to the cthode on pin 8. And the metal base is indeed wired to pin 1. OK in a 5150

[JacksonRR]

Thanks for that concrete resolution Enzo. I recklessly went ahead with the change before you posted. Happy to say it is really to my liking. I was gasing for an Engl, but not anymore. I'm so very impressed with this amplifier after the bias mod, the noise gate and the KT88s. With some things in the effects loop there's not one frequency on any of the material I play that I don't like. I can't imagine an OT change would knock my socks off either. The mods are done. Screw the choke. Thanks guys.

[JerryP]

Can't tell. They're all black inside. Special coating of Sars or something. I'm sure they can't be wired any differently and they'll be as cool as the two in the integrated quad Steve is referring to. Yeah, I just wanna do two on the outsides because they don't fit inside and the integrated quad is stupid.

Hey Jerry, I really didn't mean to ruffle your feathers. It's not about what you're doing, it's about what I'm doing. You ,as the king of 5150 mods, are the reference point. Your pdf on the bias mod is still floating around. Thankyou.

I'm not upset, I just want to be sure people understand there's a lot more that goes into it when a business does the work. For me it's not just the price of the parts. Just as Doug pointed out with the beer analogy. Some folks look at the price of a few resistors and caps and right away people want to say the shop is ripping someone off.

There are some 5150 mods posted at Rig Talk that were suugestions from Mark Cameron. They sound pretty good. Rig-Talk • View topic - 5150 mods... revealed
Jerry

[JacksonRR]

If it was the price of the materials that governed the price of the job, then drywall finishers wouldn't get paid shnit.

Also, found a post from long ago by Jerry on another forum about running KT88s. I'll get some beefier screen grid resistors in there. And Jerry, thanks for that link. The mods aren't done, I guess, lol.

[JacksonRR]

So I went to my local Fry's Electronics and they didn't have any silver mica caps for that mod on the page Jerry posted. I ended up finding this site: http://www.danscloseoutsandspecialde...cialdeals.html
Spent $30 including shipping for enough components to fill my bathtub. Plus some PCBs for pedals and whatever. I've been wanting to do a rack-mounted boost with a few options:a tube screamer circuit, a clean boost, EQ'd or linear... and a copy of the Jackson JE-1000 preamp booster. The one that changes the peak resonance freq of passives.

So silver mica caps are not polarized? I'm looking for that info right now.... And have been. Haven't found a yes or no yet.

[Steve Conner]

Silver mica caps are non-polarized. You can hook them up either way round. Electrolytics are the only polarized ones. (both the regular can type and tantalum beads)

What on earth is an "integrated quad"?

[JacksonRR]

A 5150/6505 power tube configuration offered by Eurotubes. http://www.eurotubes.com/5150EX-7.JPG
They test until they end up with a pair of 6L6GCs and a pair of either KT-66 or KT-88 that draw the same current. Seems to me things could potentially drift into the dangerous. Not that it isn't cool.... I just don't feel safe on that stunt.

[Enzo]

Yeah, he also used to sell selected pair of 6L6s with EL34s to make "integrated quads" for various amps.