HRDlxe: what can I make with it?

[GibsonGM]

Hi guys,

Just finished up my first tube build, an 18 Watter. I love that amp! Now the old HRDx's...lacking qualities...are pretty clear. I want to do something with it, Marshall or Vox maybe. Anyone know of any plans on how to "Marshallize" the thing, or maybe better, strip out the PCB and do a nice, gritty Marshall kind of PTP build using the existing PT and OT? I'm a confident builder, just not entirely comfy with how you choose the PT and OT, things like that. But look at this, now I have those and a combo cab to boot!
Any ideas/links appreciated!

~Guitar Mike

[NTBluesGuitar]

Well, I've been known to drop some Tweed circuits in them. The 5E5A/5F4/5E7 circuit works VERY well with the exisitng iron and hardware. No need to buy new transformers!



Feel free to e-mail me for layout drawings, board drilling templates, or whatever! I've helped a couple of guys with a DIY of this and they all came out just fine. A couple of other TFFers have put Bassman (5F6A) circuits in theirs...I'll let them chime in with their projects. Rob? Pete? You're up!

[wingnut1]

If the amp is working and in good shape, I would sell it and either use the money to buy a kit or the parts needed to build what I want. If the amp is broken or has a lot of problems I would strip is out and do the Bassman like NT did.

[NTBluesGuitar]

... and do the Bassman like NT did.

My particular one is the Tweed Pro (5E5A). Pete (Toneseeker) put a Tweed Bassman (5F6A) in his, and Rob put a 5F6A in his DeVille. I've also done a 5F6A in a DeVille.

Just FYI.

[Cygnus X1]

Not sure about the iron, but a Marshall 18 watt would probably fit in there. Or a high gain SEL with a tube reverb?

Check AX84 and look at some of their build designs.
Most are single ended, but there are a few PP designs.

I'm very happy with the SEL's that I have built.

[GibsonGM]

Thanks for the info, guys. The amp works fine, and I've done the Philpott mods (not the sag one). It helped, but not quite enough. Once I get my 18W head and a cab on the stage, this one is open to mess with.
I think I'd get about $400 for it; enough for a kit, but not enough for a cab, spkr, tolex etc. , which is why I'm thinking of keeping it all but the board, essentially. I like the idea of reusing the iron! And popping a turrett board & pots in seems pretty damn easy.

I'm thinkin' lower wattage, like 20-24W, so I can crank it up (the main problem this amp has now is that at 40W I am never anywhere near power tube distortion...have to run pedals, echhh). The drive channel is flabby with my LP, and quite brittle/sterile, IMHO. I'm looking for a tighter sound (the 18W is great). I don't have enough experience with old Fender's/Vox - anything come to mind that sounds like say The Outlaws, Allman's, Frampton, etc? I like hard but toneful sounds (I know that's quite a range there, lol).
I'll check out AX84, too. Something that biases itself sounds really nice, since I have no equip. to do that other than a DMM....

REALLY nice job on that one, NT!!! I will probably hit you up for more info when I make a decision...

[NTBluesGuitar]

I'm thinkin' lower wattage, like 20-24W, so I can crank it up (the main problem this amp has now is that at 40W I am never anywhere near power tube distortion...

There is a trick for using 6V6s with the amp thanks to it's OT setup...but you will have to be able to re-bias it. You put an open jack into the main speaker jack and plug the 8ohm speaker into the ext. speaker jack.

What this does, is isolates the 4 ohm tap for the ext. speaker jack. With the OT primary at 4.25K and an 8ohm load on the 4ohm tap, you've got a good reflected impedance for the 6V6s. Getting your wattage down where you want.

It's nothing to do with the circuitry, but with the way the switching jacks are used. As a matter of fact, whenever I do rebuilds of these amps, I don't even disconnect the OT wiring. So, no matter what goes into the gutted chassis, that feature is still available.

Might be something to try before you decide on the transplant.

[Cygnus X1]

Here's a link to a thread about my SEL.

http://www.thefenderforum.com/forum/...ad.php?t=39880
I want to try this circuit in push pull.

I put a 6V6 in the prototype, and I'm really satisfied with it.

There is enough tube space on HRDX to run a reverb or effects loop also. I need to record some sound clips, but halfway clean to Judas Priest level distortion is all there.

[GibsonGM]

That looks really cool, Cygnus! Another type of circuit I'd like to mess around with at some point. I'll keep an eye out for sound clips...what is the output wattage appx? I'm looking for maybe 20W or so, 1/2 of what I have now should be fine...the 18W is nice but I still have to use it with my band to see how it works out.

So NT, how can I go about re-biasing if I do the 6V6 trick? Have you done this? I'm really interested in getting the thing tighter, and at lower volume levels, with minimal cost if possible. And matching something lower wattage to the iron could be an issue, so it could be worth a shot.

The end product is that I want to run my 18W head with a 2x12 cab for real mojo, and have the combo for smaller venues where I want it all in 1 piece, with the combo HRD offering more "80's" due to what my band wants to play at times...
Thanks guys, ideas are starting to pop out...

[NTBluesGuitar]

So NT, how can I go about re-biasing if I do the 6V6 trick?

I haven't personally done it, but I've heard of plenty of folks who have. Re-biasing means adjusting the math for the plate dissipation of the 6V6s...A 6V6GT is a 14W tube; 70% of 14W is 9.8W.

[Cygnus X1]

As NT correctly calculated...that SEL with the single 6V6 is putting out around 7-9 watts. Hard to get to band-level clean with it. That's why I'm looking real hard at the 4-4-0, but that is a whole other story.

I have run a 6550 in it, still not gig-able.
My particular goal is good tube saturation at garage level.

Have you tried any tweed amps?
It depends on what sort of tone you are really after...a bassman circuit would work, but if you want Marshall type gain, then some choices have to made in the tone stack, preamp setup, etc.

[NTBluesGuitar]

A couple of guys who have done the HRD-to-5E5A claim that jumping the channels gives a Marshal-esque sound.

Here's a thread with some sound clips (post #4, second clip): http://www.thefenderforum.com/forum/...ad.php?t=38275

[GibsonGM]

Yup, that's the tone! I'd like to be able to get a little more dirt than on the HotRodblues clip, but right now I only get what he's getting at ear-shattering volumes. The "Marshallesque" sound would be a good rhythm tone for me (I play a LP and a Tele), and a booster would probably get the level up good for leads.

This is going to be in the future, maybe spring, so time to research more. I want to check into the 5E5A, see how hard it is to change over, maybe do a turret board at my leisure.

I get the concept of rebiasing, but just don't know how to do it, lol. The HRDx is easy, using voltage rather than current. I've assumed you need a special bias meter or something, but there is probably a way to do it mathematically, eh? It's one of those things everyone puts in the 'magical' category, like messing around with B+.... Like, if you get it wrong, it sounds like pure crap?

Thanks for the pointers, guys!

[NTBluesGuitar]

Biasing using the mV reading is pretty simple.

Step 1 - Measure the cathode voltage (mV) at the Bias Test Point. Write it down.

Step 2 - Measure the plate voltage (pins 3), doesn't matter which tube. Write it down.

Step 3 - Multiply plate voltage by cathode voltage (remember that 85mV = .085V). So, if your plate voltage is 415V and the Cathode Voltage is 85mV, the math is: 415 x .085 = 35.275. That's how many watts are being dissipated. The Hot Rods cathodes are connected prior to ground, so that number is for disspation of both tubes combined

Step 3 - Divide total watts dissipated by 2 to get watts per tube disspation. In this case 35.275 / 2 = 17.6375 watts disspated per tube.

Step 4 - Divide watts dissipated per tube my max plate dissipation for the tube. Assuming this is a 6L6, the max is 30 watts. If this were a 6V6, here's where you change the math and divide by 14 watts. So, 17.6375 / 30 = .5879 That's about 59% of max plate dissipation. 67%-70% is the common range folks settle on, but you don't want to go TOO much higher than 70%.

Step 5 - Adjust to taste.

As I've said, just shout at me for some drilling templates and layout notes if you go the route of 5E5A. It's a fun project with lots of room in the chassis to work with.

[yankeerob]

I'm doing a HRDx conversion using the 5E3 circuit in the new year - the B+ will need dropping around 50V but something like a WU4GB should get us in the ballpark - I'm looking forward to it!!

[GibsonGM]

Hey, thanks a lot for that easily understood description, NT. That biasing method works on *any* amp, or just cathode biased ones? Now that i've tasted blood with the 18W, I want to learn more about the finer details, lol. Sort of like setting the emitter resistor on a BJT?
I would love whatever info you have (layout, drilling template for sure)!
I'll drop you an email. Thanks again, I've noticed that you help a lot of people on this forum...cool....