Regal Model 500

[Toxophilite]

I have this Regal Model 500 amp I bought 10-12 years ago for $6. My brother has had it for the past 8 years or so but lately it has been a stand for the $20 champion 600 I found a couple years back so I reclaimed it. It's a funky little amp but has never had the sort of tone controls I've found useful. I'm not really a no knob/1 knob tone control guy.


I was wondering if anyone had any suggestions for maximizing the clean potential, making the tone control more versatile(there are 4 inputs and I only need 1, so a tone control could be added)


Maybe beefing up the bottom end, making the top a little crisper.


The tremelo is very cool


obviously a speaker change is an easy modification


It has the worlds smallest IT, that could be a source of bigger/cleaner sound with an upgrade.


Everything seems to be working.

[Toxophilite]

And of course the schematic that wouldn't fit in the last post

[Toxophilite]

As I'm not an electrical engineer, on thing that confuses me abut this design is the 2 capacitors separated by resistors to ground between the 1st and 2nd gain stage. I understand one capacitor.
This seems like an effort to tame the front end of the amp
yes?


Interesting there are no bypass caps on the 2nd stage(driver) and the power tube cathode resistors.
In this link a fellow is suggesting putting a bypass cap on the 6aq5s cathode resistor
https://www.premierguitar.com/articles/24948-ask-amp-man-restoring-a-worn-regals-royal-tone
I alligator clipped on in and got a lot more gain, almost like deactivating an NFB loop, which interestingly this amp doesn't have.


Any ideras

[DummyLoad]

2 pole hi pass - steeper low freq. roll-off.


--pete

[DummyLoad]

clip in a 1u or 2.2u bypass for V3. that'll surely wake it up. it's a fender champ-like amp with a 1/2 james stack (treble), a-la fender 5E3, etc..  trem oscillator V1wobbles V2 cathode by sharing Rk; you enable that action by shorting across R3 (33k). they must have gotten a sweet deal on a truckload of 6AV6, could have replaced 2 6AV6 with 12AX7 and saved $$ on the extra socket. 


--pete 

[Toxophilite]

2 pole hi pass - steeper low freq. roll-off.


--pete

Are you referring to the 2 cap and resistors deal between V3 and V4?

[DummyLoad]

2 pole hi pass - steeper low freq. roll-off.


--pete

Are you referring to the 2 cap and resistors deal between V3 and V4?


It'd be nice to bring some of that bottom end back in if the amp had an OT to handle it.

yes.

[Toxophilite]

It'd be nice to bring some of that bottom end back in if the amp had an OT to handle it.
MAybe get rid of half that 2 pole hi pass?


Do you think I could get away with putting the other half of the Baxandall/James in there?I could use one of the 4 input jack holes or build it right next to the 'treble' pot

[DummyLoad]

It'd be nice to bring some of that bottom end back in if the amp had an OT to handle it.
MAybe get rid of half that 2 pole hi pass?


Do you think I could get away with putting the other half of the Baxandall/James in there?I could use one of the 4 input jack holes or build it right next to the 'treble' pot

not with good results. likely too loss-ey with full bax/james. OT is the achilles heel in that amp, and probably why the steep low freq pole of hi-pass to keep from saturating puny OT. then again, it is probably only making about 3.5W. NFB may be of benefit to tighten up the bottom.

OTOH, good bottom end takes power: that amp is lacking in that department. respectfully, this amp is nothing more than a cheap pile of parts. mod it for more gain, replace the speaker with something more respectable and flip it to a blues hound for a profit. build something better?

--pete

[Toxophilite]

Hilarious! I love your blunt yet undeniably truthful assessment!


I did think of picking up a Hammond Champ Ot
I could scoff  a way better one out of a roberts reel to reel amplifier (SE 6BQ5) I have and give it a try for kicks but it might be like trying to dress up a pig..still a pig!


I do kind of like the cabinet, with some corner bloclks glued in it would be a sturdy yet light little ply cab and it could take a baffle for a twelve if so desired


One thing I thought of doing with the amp is nuking and paving as my brother says
Use the PT maybe and the chassis and some other basics and do a complete rebuild inside of it.

[PRR]

{as said} The tremolo thumps. The C-R-C-R helps to cut the thump.

If you have not guessed:

This is "a Champ", only even cheaper. Those triodes "are" half of 12AX7, and the year transistor radios killed tube radios two 6AV6 might have been cheaper ($0.33/ea) than one 12AX7 ($1.77/ea). 6AQ5 is of course 6V6 curves in a significantly slimmer jar and guts.

Essentially "all" Champ ideas can be thrown on the wall to stick/slip. The AA Champ has Bass and Treb, and you can add a Mid same as the bigger blackface amps. Better (or worse!) OT is always something to try. **Speaker Very Important!** The stock speaker looks like a low-low-bid ceiling speaker. Jumper the amp to a decent half-stack and it may grow some balls (or not, if the crap OT is stunting it).

[jjasilli]

Ditto to speaker upgrade.  Re tone circuitry, I suspect the amp may sound good as-is, though maybe different.  To me, that's a good thing.  Possibly the T-filter is working together with the TS, so that changing just one may lead to imbalance.  I guess Dummyload already said that in a different way.  You have the option to convert this into some kind of Champ / early Princeton / Harvard clone.  My personal preference is to enhance what's already there, if it even needs enhancing.

[jjasilli]

. . . OTOH, radical re-builds have occurred to me.  Replacing the preamp tubes (& sockets?) with twin triodes like 12a_7's, lots of options arise: cascading gain stages per Marshall or Mesa Boogie; cascode input stage; '59 Bassman preamp & CF TS; etc.

[Toxophilite]

Thanks for all the ideas!


I think a proper recap to start with would be good as there's a bit of distortion most of the time even trying a different set of speakers (the 2 10" eminence alessandros in one of my vibroluxes so decent speakers) Also check some of the resistors for value drift.


What I'd like to achieve is something that could give me pleasing apartment CLEAN practice volumes but also something that could be used in a studio application of I want the distorted sound of a small amp cranked.
Maybe a tone stack with a bypass switch?


As it is the tone stack gives me very mid heavy sounds. Something I'm not to keen on generally. I thought with a baxandall I could scoop some of that out. If you turn the treble down it gets muffly, turn it up and ti's pointy and evil. Never has much bottom and never really achieves a 'nice' sound , even though nice speakers.


I was hoping to find an old single ended reel to reel OT or hifi locally but not much around. I could order a champ one from Hammond for not too much. Humourously I've sold several over the past few years. NICE ones . philips, telefunken etc. 


Which has more insertion loss baxandall or fender AB763 tone stack?
My guess is the fender circuit.

[jjasilli]

I think a proper recap to start
Agreed. First order of business should be to get it working right.  Maybe you'll like it.

Baxandall has least insertion loss.  Baxandall is "mid heavy", 'cause the FMV mid dip is not there, which we all got used to.  Some people prefer Baxandall. 


Baxandall is common in hi-fi, but there's usually bass & treble controls.  A mid control is considered unnecessary, because you can emphasize or de-emphasize mids by turning the bass & treble pots up or down together.  So, 1/2 a Baxandall isn't very helpful, since you can't get rid of the mids. 

Some amps like the Ampeg V4 have a Baxandall TS sporting a mid control knob with SWable center frequencies.  The -0- position for all 3 tone pots is 12 o'clock!

[Toxophilite]

THough a nuke and pave might be in order
I thought since my initial investment was $6, paying for a Hammond champ OT(can't seem to find an old reel to reel locally!)
a 12ax7 socket and the parts for a AB763 tone stack might not be too crazy a splurge.
I have a variety of speakers i can try in it, making a new baffle would be easy.


I was thinking a 12Ax7 instead of V4 would give me another gain stage to compensate for the AB763 insertion loss as well as allowing me to achieve some more of the (apartment level) clean sounds I desired.


I could probably build a princeton or some sort of 6BQ5 pushpull amp in it too if i wanted but them maybe I'd have too much amp for the intended purpose.(I have transformers that would work for that though so the cost would just be the other components)

[Toxophilite]

For fun I swapped in the SE 6BQ5 OT from a roberts reel to reel preamp/amp
It's about 4 times the size of the tiny thing the Regal has.

Not surprisingly it sounds way better with a nice round bottom end
It was kind of small, nasty and distorted sounding before, even at lower volumes.

The loner OT is the big one by the PT the original Ot is the chiclet on the right.