1st build hemming and hawing

[Scooter Thomas]

Well, I knew joining TAG would force the issue. I gotta build an amp!

I mostly play a JTM45. I don't "need" a guitar amp, but I could use a Rocket or a 5E7 or 5E8A. What I do need is a Dynaco ST-35 or maybe ST-70.

Still, I think I'll build a 5F1 to start. I'm thinking I want the Triode kit with the 15w OT and a KT66 (10w cathode cap) with a 10" speaker (Weber 5F2A cab.)

So ... do I want to use the 8k or 5k OT primary?

Room for a 3-way rotary for impedance select?

Will a KT66 perform ok in this circuit?

Orange drop or Mallory?

Anything else I should consider?

BTW, I solder by numbers. I can discharge caps, I have a snuffer stick. I have a lightbulb limiter I built and used when I swapped my JTM PT. I'm not much of a circuit jockey and my limited tools are abysmal but functional. I don't have a bench with a variac and iso transformer but I can safely wire a champ, I think!

[Cliff Schecht]

For a higher output power tube I would use 5k. That 5k is good for a 6V6, 6L6, EL34 or any derivative thereof really. There are ways of actually calculating what the optimal xfrm impedance should be but IME 5k is great for SE amps.

There is always room for a 3 way impedance selector! If not I prefer only 4 or 8 Ohm taps. 4 can drive anything (i.e. 4 8 or 16 Ohm speakers) but 8 is more universal.

KT66 will work fine. Might be kinda puny without 400V+ on the plates.

I don't buy the orange drop juju. I use Mallory 150's exclusively because they're inexpensive and work/sound great. I haven't had one fail or cause any issues yet. The small size is another plus.

Even though a 5F1 is a simple circuit, I'd still use a turret board and mount everything to that (as opposed to no board and straight point to point, this gets sloppy quickly). This way you aren't unfamiliar with turret/eyelet boards, how to mount them and mount components to them when it comes time to build a bigger amp with more parts.

Also like I said before, you will gain power output with a higher B+. This means you have to modify the rest of the power supply to deal with the higher voltage, but that's not hard to do.

You'll run into some little issues that you didn't even think to consider most likely. We all do while learning. Don't be afraid to ask questions! Don't be afraid of messing things up either, again if it comes to that point you have this whole forum to help out. Usually a description of the problem and a few pictures are all we need to diagnose problems.

Good luck buddy!

[Phil_S]

Well, I knew joining TAG would force the issue. I gotta build an amp!

Welcome. Be careful what you hope for. Amp building is addictive. After you build one, you'll never get the monkey off your back. You can, however, moderate how often you need a fix.

I mostly play a JTM45. I don't "need" a guitar amp, but I could use a Rocket or a 5E7 or 5E8A. What I do need is a Dynaco ST-35 or maybe ST-70.

That's not right. Everyone needs another guitar and another guitar amp. Stop kidding yourself. This isn't about what you can use. After you build one, you'll understand this truth better. It's the Dynaco's that are nice to have. Either way, learn how to do it and you can build what you like.

Still, I think I'll build a 5F1 to start. I'm thinking I want the Triode kit with the 15w OT and a KT66 (10w cathode cap) with a 10" speaker (Weber 5F2A cab.)

This is a good place to get your feet wet. A relatively simple amp like this will still teach you more than you imagine.

Room for a 3-way rotary for impedance select?
Will a KT66 perform ok in this circuit?
Orange drop or Mallory?
Anything else I should consider?

Cliff covered this nicely, IMO.

BTW, I solder by numbers. I can discharge caps, I have a snuffer stick. I have a lightbulb limiter I built and used when I swapped my JTM PT. I'm not much of a circuit jockey and my limited tools are abysmal but functional. I don't have a bench with a variac and iso transformer but I can safely wire a champ, I think!

You don't need fancy tools and diagnostic equipment to get started. Everyone starts with the bare essentials and soon you'll stop soldering by the numbers!

Get going on this! We want to see pictures of what you do.

[Scooter Thomas]

The Triode kit is turret board so, yeah Cliff, I'll certainly benefit from that experience.

Instead of the rotary impedance, maybe I'll just add a jack since I only need 4 and 8 ohm.

Properly driving the KT66 is my main concern, I really want that rounder sound plus I have a Gold Lion that needs a home.

I should get this going in a couple weeks. Damn, I haven't ordered parts and I'm already strung out!

Thanks guys. Can't tell you how much I appreciate the help and encouragement.

[echuta13]

The Triode kit gives you the option of upgrading the transformers. I would suggest upgrading both. The upgraded output transformers offers 5K & 8K taps, and higher ma rating. The power transformer upgrade gives you higher ma rating as well with additional voltage options. Both would be very good if you wanted to switch between a 6v6 and KT66.

[M Fowler]

Yup and you can put those two different OT taps 5k and 8k on a switch.

[Scooter Thomas]

The power transformer upgrade gives you higher ma rating as well with additional voltage options. Both would be very good if you wanted to switch between a 6v6 and KT66.

But the flux band on the ClassicTone 40-18019 looks so cool!

Decisions decisions. Frankly I'd like to save the $16. Cooler operation and improved regulation is good, but I have no reason to think the 40-18019 would run excessively hot or be poorly regulated.

What I don't understand is how I might use the 550v secondary (did I say that right) on the 40-18027.

My ultimate goal is to make a KT66 happy, but I will also run some 6V6s I have on hand.

And thanks for pointing this out. I had completely missed the 30ma difference.

http://www.classictone.net/40-18019.pdf
http://www.classictone.net/40-18027.pdf

[Scooter Thomas]

Yup and you can put those two different OT taps 5k and 8k on a switch.

Easy enough. Would that like change the output power, what would it do?

Gawd I feel ignorant,

[M Fowler]

Quick change out 6V6 8K vs. 6L6GC 5k flip the switch and pop in the correct tubes.

But keeping it simple is the best way to go 5k primary OT and like Cliff said you can run all the various tubes 6v6, 6l6, kt66, or EL34.

[Cliff Schecht]

Don't feel ignorant, these are topics that fall under general electrical engineering theory and take many people years to fully understand/master.

The output power will change so very slightly, what you are more likely to hear is a difference in the tone. The higher output impedance will tend to darken things a bit (for a few reasons) and smooth out high end, which can help if you don't use negative feedback in the power stage.

To really increase the output power, you need to increase the bias (only can do so much here, even more limited with cathode resistance based biasing) and increasing the power tube plate voltage. Another 100V or so on the plates will gain you 10-12W which is only a small percentage of a power increase. To get twice as loud you have to increase the power 10 fold (i.e. 10W is 10dB of power and 100W is 20dB of power).

[M Fowler]

These little single ended amps are a lot of fun to play through don't sell them short. Playing with different tubes can really bring out the amp. I played a sweet old Fender champ with a 6K6 power tube and it was fantastic better then an old gray RCA 6V6 tube.

[Cliff Schecht]

Oh yeah, and my little "secret" for getting Champ style amps to really rip is to lift the tonestack. You get a huge signal boost which really lets the simple topology distort pretty heavily without needing any pedals. All of my Champs get a tonestack lift (as well as a switch to engage/disengage the NFB).

[Scooter Thomas]

Quick change out 6V6 8K vs. 6L6GC 5k flip the switch and pop in the correct tubes.

But keeping it simple is the best way to go 5k primary OT and like Cliff said you can run all the various tubes 6v6, 6l6, kt66, or EL34.

I didn't understand how load resistance was determined for a given output tube then it dawned on me, it has to be a parameter set by the manufacturer. Doh!! I looked at some tube data sheets and I think I kinda understand. It appears plate load resistance increases with plate voltage. So, looking at the 6V6 data, with 250v plate load resistance is 5k ohms, at 315v (at least what we're using) load is 8k5 ohms. The KT66 load is 2k2 ohms at 250v.

I'm definitely doing the tap switch.

I came across this pretty good page about determining specs for unknown transformers.
http://www.radioremembered.org/outimp.htm

If, ultimately, I get plate voltage up around 400v for a KT66, won't that slay a 6v6?

Also, maybe I should clarify. I'm shooting for a classic champ vibe, just a little broader in the shoulders, so to speak.

[Scooter Thomas]

All of my Champs get a tonestack lift (as well as a switch to engage/disengage the NFB).

I don't recall ever reading about folks tweaking NFB on a champ, so I was surprised to see it on the layout. I just never thought about. That was the first thing I thought: does anybody ever lift it? I'm thinkin' that might be pretty ragged and maybe good ragged?

[playonit]

My first build was a 5e7 head that I use through a 2/12 cab... Looking back I can't think of a better 1st build.. not complex so it is an easy build pretty straight forward if you have to trouble shoot... uses inexpensive Magnetic components iron.. and you would have plenty of room for the selector switch... Clean and chimey down low and a nice rich crunch past five... and after the build it's a good amp to add a couple of easy mods that add a little bit to the circuit... of the amps I've built this circuit is my favorite suiting my playing tastes..