Finished Gibby GA77 scratch build

[Willabe]

I just finished wiring up and test playing through this GA77 build.   

No smoke, biased up to 35mA's per 6L6. Both channels work with all 4 hi/Lo input jacks.

But, the bass control is not right, I can't really hear any difference from 7:00 (off) to ~3:30 then all of a sudden ~4:00 all the bass disappears. Happens on both channels. Doesn't matter where I set the Mid pot, even with the mid pot off, same bass 'cliff' drop off. 

Amp sounds pretty good with my strat through a Tubby tone 12" alnico hemp cone speaker in a 1x12" Mojo open back cab and my stand alone Fender reverb clone. Get the volume up to ~1:00 to 2:00 and its right there with early 70's breakup/distortion/crunch, but not over the top at all.   

The treble pot seems a too touchy, either not bright enough then too bright. But it may have to do with the bass pot problem.   

PPIMV works but it works Waaaay too fast, full up/on is 5:00, turn to 3:00 way down in volume and I have a PEC audio taper pot installed.

And the presence pot really doesn't do much at all, I (think) I can hear just a slight difference only at the 2 max extremes, 0/10.

I'll be back with some pictures and post them along with all voltages. Only 1 dcv seemed a little low, that was on the PI driver, all others looked pretty good.

Here's the working schemo posted below, all values correct.

Link for the Gibson schemo;

http://el34world.com/charts/Schematics/files/gibson/Gibson_GA-77.pdf
(Edit: Sluckey posted a link to a much better schemo in reply #4, thank you Sluckey.)
                   

                         Brad     

Edit; Fixed 2 of 3 K bypass cap values.

[eleventeen]

Interesting project. I have to say it sounds like you have pot-taper issues, but it looks from your dwg like you have them spec'ed and thus you have checked them. Do you need a *reverse* audio for the bass?

[Willabe]

The Gibson schemo lists the bass pot as 1M audio.

It doesn't do much of anything I can hear from 7:00 (off) to 3:00 and why would all the bass end fall off a cliff at ~3:30 rotation?


                 Brad   

 

[eleventeen]

The treble control is treble "CUT" implying turn clockwise = LESS treble. Yet the bass control is "BASS" implying...turn clockwise = more bass. Seems kind of...odd.


Just sayin' (about the taper thing) this is general effect when the wrong type of taper is installed in a circuit. With the wrong taper, it's fairly common to have all the usable range crammed into 20 degrees of the pot's rotation.

[sluckey]

Here's another schematic. It shows the presence pot to be only 50Ω. It also has the off-stby-on switch wired correctly.

[Willabe]

Camera battery is charging.

Here's another schematic. It shows the presence pot to be only 50Ω.

Thanks!

Doh!!!!!! Yeah, 50 ohms L ohm instead of 50KL is a horse of a different color.       

What value R do I need to put across the 2 ends of that pot to make it a 50 ohm?

It also has the off-stby-on switch wired correctly.

I did notice that the standby was drawn wrong on the schemo I was using. I wired mine up like a Fender with the 1st 2 caps always powered when on and in standby, between the 5V4 and choke.

But I can't use the standby like it is because the filter caps are 450v and in standby their getting 475vdc, falls to 420dcv in play with 35mA for each 6L6GC.   

I'll address that latter.


                  Brad   

[Willabe]

The treble control is treble "CUT" implying turn clockwise = LESS treble. Yet the bass control is "BASS" implying...turn clockwise = more bass. Seems kind of...odd.

I don't understand that. In the schemo as you rotate the treble pot towards the x end it goes closer to the treble 50pF cap, less resistance to full up no resistance between the 50pF cap and the wiper which goes to the PI input.


I'll go check the tone stack wiring and pot values/tapers with my meter. I checked every part value as I installed it so I wouldn't have any problems, but.......   

                       Brad   

[sluckey]

What value R do I need to put across the 2 ends of that pot to make it a 50 ohm?

A 50Ω parallel with 50KΩ will give you 49.95Ω.

I'm guessing you don't have a 50Ω pot? To test it I would temporarily replace the 50K pot with a switch and a 47Ω. Flip the switch back and forth and see if you hear a difference. I'm thinking you won't be able to hear much if any change.

With that 100K there's not much NFB going on in this amp. Maybe 5K would be more appropriate. I did notice that the other GA77 versions don't even use NFB.

[HotBluePlates]

The Gibson schemo lists the bass pot as 1M audio.

It doesn't do much of anything I can hear from 7:00 (off) to 3:00 and why would all the bass end fall off a cliff at ~3:30 rotation?

Lemme guess... If you have the switch at the Bass pot open, the tone stack sounds fine?

[Willabe]

I'm guessing you don't have a 50Ω pot? To test it I would temporarily replace the 50K pot with a switch and a 47Ω. Flip the switch back and forth and see if you hear a difference. 

I don't think I do, I'll look or try the R/switch if I don't.

I did notice that the other GA77 versions don't even use NFB.

Yes, between the GA77 and GA70 there's 4 or 5 deferent versions, earliest 1's had octal's for the pre tubes. 

With that 100K there's not much NFB going on in this amp. Maybe 5K would be more appropriate. I'm thinking you won't be able to hear much if any change.

Tone Quest Report mag when they reviewed an old GA77 said they thought the presence didn't do much. I talked with the guy who owned Buffalo Amps (Gibson clones) and I asked him about the presence, he it works fine, so........     

It caught my eye when I saw you recently post about having to adjust the -FB loop on the 6V6 Plexi so you could hear it.

I've never owned/built an amp with a presence and I'm not sure I'd use it anyway as I like a rounder, smoother tone, with some chime but less biting tone. I put it in just to see how it would sound and if I was missing something, so no big thing to me. I like my 5G9 a lot and it has no -FB.


                    Brad   

[Willabe]

Lemme guess... If you have the switch at the Bass pot open, the tone stack sounds fine?

No, sounds/adjusts very much the same in both positions.

I have it wired as drawn and the treble increases as you rotate clockwise but the bass decreases as you rotate the pot clockwise with a very funky bass drop off at 4:00.        

Gibson had the bass pot '0' end grounded, not stacked on the mid range 10R. This is the TS that Vox copied for their 'top boost' circuit.

There's a (slight) disagreement about if Gibson's schematic was drawn incorrectly or if Gibson actually wired them as drawn.

I asked Robert Chwaliszewski (very nice guy) the owner of Buffalo Amps (Gibson clones) about this and he said the 1's he had his hands on/in were indeed wired as drawn. He said it was just a different way to wire up a TS and that when setting the tone controls they respond different then a Fender TS.     

After checking my wiring and pot values/tapers I'm very confident it's all correct. Then I played the amp some more and I think a couple of things;

1. I think this amp's TS is very touchy. More touchy that any amp I've owed/build, which is not many. It adjusts nothing like my BF SR or my BF PR.

2. I'm playing in my garage shop which is fully dry walled so all hard reflective surfaces. It would probable sound much better in a much larger room. Right now it has a lot of bite/presence, not chime, and that's with the presence full off.

3. This amp was voiced, by Gibson, for an alnico Jensen 15" speaker, I'm playing/testing it through a Tubby Tone 12" alnico hemp cone.   

4. I haven't played a 35W amp in a looooong time, so that may be in play with what I'm hearing?

I'm going to try the WGS alnico 15" that I bought for this amp and see how if that helps. Then I think I might rewire the TS like a Fender and see if that is more to my liking. I'll sleep on it.

The amp does sound very good but I'm having a hard time dialing in a tone I like. To get enough treble so it's not muddy then there's tooooo much bite for me. The mid boost seems to be working nicely but I'd like to more chime with less bite. I should say, I really do think someone else would love it.


                           Brad      

[Willabe]

DL was kind enough to draw up a way to switch the Gibby TS to a Fender style TS, with 3P2T switch.

I did not wire it up as he suggested, I took the easy way. I might try what he drew up.


                    Brad     

[DummyLoad]

SIM shows same behavior - if bass is wired *like* a volume control, e.g. pin 3 is top, 2 wiper, 1 gnd, then results are less bass when full up.


solution: reverse 1 & 3 of the bass control. SIM bode plots shown have correction.   


--pete

[Willabe]

solution: reverse 1 & 3 of the bass control.

Thanks Pete.

Easy enough to fix.


                  Brad     

[Willabe]

With that 100K there's not much NFB going on in this amp.

Hmmmm, maybe I do need to add some -FB to tame the bite?

I think I'll try that 5K -FB R.


                       Brad   

[Willabe]

Pictures below, warts and all.   

All in all I feel it's not bad, it's the largest, most complicated build I've done. It was difficult to see the whole thing in my mind when I was drawing out the layout. I would do several things a little different but hind sight is always 20/20.

        Brad     

[Willabe]

I had to tack in a tail R for the -bias to get into the right range from my schemo's value, you can see it in the bottom pic, I'll take it out later and put correct R value in.

 

[SILVERGUN]

Great news that you've gotten this far.....
For all the time you've spent helping others, it's amazing that you had time to twist all of those wires! 

NICE PICS!!
 

 
 

[Willabe]

     Thanks Dave.


           Brad   

[PRR]

> It shows the presence pot to be only 50Ω.

That seems unlikely.

Gain from that point to speaker is only about 7. Maybe 50 at speaker bass resonance.

NFB resistor is 100K.

To-ground impedances smaller than 2K are same-as a short, zero NFB.

You can't fake a  50Ω pot with a 50K.

My guess, from similar plans, is the presence pot could be 5K.

[sluckey]

I think I'll try that 5K -FB R.

I wasn't very clear on that point. I meant try a 5K pot. I'm still thinking you will need to decrease the 100K series resistor to be able to hear much change on the presence control. That's what I had to do on the plexi6v6. End results was a 22K series resistor and 5K pot feeding into a LTP PI. Then I had a noticeable change in presence when adjusting the pot, but more important, I was able to clearly tell when the polarity was correct.

My plexi values will probably behave very differently in your amp, but the idea is to experiment with values. Gibson was never very picky or consistent with this stuff. 50Ω pot working with a 100K series resistor is really more improbable than 50K pot with 100K series resistor. That's why I was suggesting a 5K pot. The main thing is get enough NFB going so you can verify if it is proper phase. At that point, some of your tone control issues may become non-issues too. 

[Willabe]

Thanks PRR and Sluckey.   

This amp is said to be Gibson's attempt at going towards a Fender type sound, the closest they came to it back then and a very different sound, much brighter, than Gibson's line up to that point.

The main thing is get enough NFB going so you can verify if it is proper phase. At that point, some of your tone control issues may become non-issues too.

Ahhhhh!

My guess, from similar plans, is the presence pot could be 5K.

DL (Pete) pointed out early on that this amps power section is very close/the same as Fender's big tweed 6L6 5E _ _ series with a cathodine PI with -FB, before Fender went with a LTPI, big 5F _ _ series. Plus it has the same CF driven TS, although Fender used different tone control circuits, (more hi-fi type?) but Fender did use local FB around the CF and it's driver where Gibson did not.

Fenders tweed 6L6/6V6 5E _ _ series, -FB loop/presence values, all with 1K5 K/R on 12AX7 cathodine PI driver where -FB is applied, same 1K5 K/R as GA77 driver, but Gibson used a 12AU7;

5E4, 5E4A, 5F4, Super (6V6's), all; -FBR 56K, pot 5K, cap .1, 4 ohm tap.
5E5A, Pro; 100K, 5K, .1, 8 ohm tap.
5E6, 5E6A; Bassman; 20K, 5K, .1, 2 ohm tap.
5E7, Bandmaster; 56K, 5K , .1, 3.2 ohm tap.
5E8A, Twin; 56K, 5K , .1, 4 ohm tap.
5E11, 5F11, Vibrolux (6V6's), both; No presence control; 56K, 8 ohm tap.

So, I have a PEC 5K pot and I think I'll play with that per Sluckey's and PRR's input.


                       Brad     

Edit; Added -FB ohms tap values and Fender (12AX7)/Gibson (12AU7) PI tubes as per what terminalgs brought up.         

[HotBluePlates]

DL was kind enough to draw up a way to switch the Gibby TS ...

I did not wire it up as he suggested, I took the easy way. ...

The 2nd drawing looks effectively like what you have in the schematic in the 1st post. Which to my eyes looks like a Fender-style stack if the connection from Bass control to ground is open. That's why I asked if opening the switch made it work better (because then it seems like it should behave like Fender).

If that's not what you built, -25 points for posting a schematic that's not what you made. 

[terminalgs]

regarding the presence/NFB,  the 100K and the 1.5K cathode resistor under the 12AU7 are the dividers for the NFB.  Given that the closed loop gain of this amp with a 12AU7 is low (compared to other amps), and that the NFB comes off an 8ohm secondary,  100K and 1.5K seem like they might be about right, tho I haven't done the math (I imagine Gibson wanted plenty of NFB). 


with a presence control pot of 50ohm, it seems like the .1uf would "be in play" all the time. 5K is enough to effectively take the .1uf out of the equation. its easy enough to test with a switch under the pot.

Its a good idea to set up a couple pots and/or switches to tune nfb and presence, like sluckey suggests.   temporarily replace the 100K with a 500k or 250k pot. (I don't think you'll end up anything lower than 100K, but you never know). you could also try different caps if you want more or less presence effect on the NFB., or remove it entirely if you don't want any presence.

[Willabe]

The 2nd drawing looks effectively like what you have in the schematic in the 1st post. Which to my eyes looks like a Fender-style stack if the connection from Bass control to ground is open. That's why I asked if opening the switch made it work better (because then it seems like it should behave like Fender).

Yes, with the switch closed it's stock Gibson, open it's Fender TS. The 2nd drawing is how it is wired up.

That is why I added that switch to see if the 2 TS sounded and/or acted any differently. I figured for the cost of a small switch why not try it out?

But it's not doing anything that I can hear at this point.


             Brad     

[HotBluePlates]

Like DL said, simulating the circuit (for me in TSC) does exactly what you describe. With Fender-style wiring, all the action is between 0-3 (out of 10) on the Bass pot.

Note Fender used 250kΩ pots here for both Treble and Bass. Plugging those back into the TSC, the action becomes a lot smoother.

[Willabe]

regarding the presence/NFB,  the 100K and the 1.5K cathode resistor under the 12AU7 are the dividers for the NFB.  Given that the closed loop gain of this amp with a 12AU7 is low (compared to other amps), and that the NFB comes off an 8ohm secondary,  100K and 1.5K seem like they might be about right, tho I haven't done the math (I imagine Gibson wanted plenty of NFB).

Thanks terminalgs. I went back an added the ohms tap values and PI tubes to the Fender -FB loop values in reply #21.


                     Brad   

[DummyLoad]

GA77 TS IMO, is not so good. there is a dip peak (-30dB) at ~500Hz. with the bass and treble at 100% of rotation. with the bass and treble at 50% of rotation, the dip peak (-20dB) is at ~633Hz.


attached are two schematics. switches in the position shown are for the stock GA77 TS operation. the second shows the switching arrangement in alternate mode that parallels treble cap and treble pot and enables the mid pot, with the results similar to the AB763 TS, not exactly, but close enough. when in AB763 mode, the mid control boost is significant.


will post bode plots of GA77 TS and "hacked -up" AB763 later when time permits for comparison. right now i have dinner plans...


--pete

[terminalgs]

nice pics BTW!!  very organized and tidy.

[Willabe]

nice pics BTW!!  very organized and tidy.

Thank you.       I feel I'm getting a little better with each build. I just need more experience but I don't build much. I do have a few new things in mind though.   

If and when I get my builds to look as good as Doug's and Sluckey's then I'll be happy.


                  Brad   

[Willabe]

GA77 TS IMO, is not so good.

DL, you had this amp on your zilla breadboard and IIRC you really liked it, especially when using the bigger Fender (SR) iron?

Do you remember which TS you used?


              Brad   

[DummyLoad]

i remember ordering 2ML pots to satisfy the proof of the first controls. i recall the tone stack was just OK and i believe that i ended up with a modified arrangement of GA77 TB.

link to the TS i liked. 

http://el34world.com/Forum/index.php?action=dlattach;topic=14835.0;attach=35294

link to the POC thread.

http://el34world.com/Forum/index.php?topic=14835.0

fiddle with the treble cap and treble pot values and wire the bass as in the linked schematic above. use the switch to move from the fixed 10k mid to the mid control pot. easy fixes.

--pete

[Willabe]

Man, this amp is loud!!!!!! I've forgotten what it's like to play this loud.   

Ok, I just changed out the 50K presence pot for a 5K pot, better, over all.   

Presence is starting to work, I can hear some difference now.

Also, the tone controls are working a little better and I can hear a slight difference when I flip the TS bass pot grounding switch. PPIMV is a little better, doesn't drop volume as fast as before, still too fast though. It's 250K dual pot, might need to change it to a 100K dual pot or maybe just wire it up like a LarMar?. It's not wired as a LarMar. (see schemo) (So I think you and PRR were right Sluckey.)

Over all the amp's tone is a little smoother, rounder and less harsh with a little more chime and less bite. Definitely going in the right direction but still not there yet, for what I like anyway.

For the 5E5A Pro, Fender used; 100K, 5K, .1, 8 ohm tap, with a cathodyne PI but with a 12AX7 for the PI. I would think there presence control worked fine? terminalgs must be right about the 12AU7 PI giving less gain in the -FB loop and that would be why Fenders values worked with the 12AX7 PI but in this the Gibby the 12AU7 isn't working as well? Maybe I'll pop a 12AX7 in to see/hear what happens?

I'm going to try what Sluckey suggested and add some more -FB by changing the 100K -FB R to ~50K (have to see what I have on hand) to try and see if; 1. I have the OT leads backwards and 2. See if I can get more response from the presence control.

Then I'm going to try it through the 15" WGS alnico and now that I trust the amp, put in a NOS set of Phillips JAN 6L6GB's. I have EH 6L6GC's in there now. Then also try a 12AX7 in the 1st preamp position as I've never liked a 12AY7 in that same spot in my 5E3 and 5G9.   

Then if still necessary, I'll rewire the TS like a tweed or a AB763. Or maybe like DL posted?

I still haven't tried my LP with HB's through it yet.


                         Brad   

[Willabe]

i remember ordering 2ML pots to satisfy the proof of the first controls.

I found a NOS J type that is 2.25ML and that control works just fine, no problems there. I could see it being very useful with a dark sounding guitar if you wanted to brighten it up.


                     Brad     

[Willabe]

All right just did the math for 70% bias, and it comes out to ~53mA's, each. I was at 36mA's, each, ~50%.

EH 6L6GC; 30w/396.6dcv= .0756x.7= .0529mA, dcv. Sounds a little better, a little fuller/warmer, not a ton.

Then I put in a 12AX7 for the PI instead of the stock 12AU7 and it did make the presence control more noticeable as you rotate it but not a lot more, still pretty subtle. But it does make a difference in tone that you can hear, more like tweaking the amps overall sound/response not drastic in your face change. (It was just a test, I put the 12AU7 back in and it will most likely stay there, the 12AX7 gave the amp too much distortion for me.) 

But then I put in a re-issue Tung-Sol 12AX7 (I can't find the other 2, 3 NOS 12AX7's I have     )   instead of the NOS 12AY7 and Whaaaammmm!!!!! MUCH better! MUCH happier with the amps sound now!   
 

I was starting to get worried I wasn't going to like this amps tone, for me any way.

The chime that was missing is now all there and it's fuller/rounder and that's with the mid (boost control) full off. (I don't know why but I've never liked the sound of a 12AY7 in my 5E3 and 5G9, they sound dull and kinda lifeless to me.) The notes seem to sustain more and with my picking attack they seem to jump off the fret board instead of just lying there? Hard to describe but I can hear a BIG difference and I 'feel' a big difference when playing. I'm not setting the volume past 5 to 6 on this amp (and the same thing happens with my 5E3 and 5G9 at 3.5 to 4.5) so it's still on the 'clean-er' side with my strat.

Next, I'll try a Ken-Rad NOS 5V4 with a NOS matched set of Phillips JAN 6L6GB's.

Then the 15" WGS.


                    Brad                      

[Willabe]

Ok, I put in the Ken-Rad NOS 5V4G and the Phillips JAN NOS 6L6GB set and biased them up to 44.1mA each., ~60%.

Wall voltage ~123.5acv;

Ken-Rad NOS 5V4G; pin 8; 420dcv

biased at 44.1mA, each, (the bias/balance works great, very easy to get within 0.2mA's between the pair and I really like the tip jack set up.)

Phillips JAN NOS 6L6GB; pin 3 (plate); 394dcv, pin 4 (screen); 394.5dcv
                                    pin 3 (plate); 395.4dcv, pin 4 (screen); 394.2dcv

Sovtek 5V4; pin 8; 420dcv (got this tube from Doug and it's right on the $$ for rectified dcv compared to the NOS.)

I think I might like the EH 6L6GC's a little better, a little cleaner and firmer. I have a set of -C- 6L6GC's that I bought several years ago, I'll try those too.

Big surprise, when I put in the JAN/Phillips 6L6GB's I put the NOS 12AX7 GE into the 1st preamp position and the new Tung-Sol into the TS CF position and although the GE still sounded better to me than the NOS 12AY7, more chime, it lost some chime and fullness. Flipped/flopped the 2 and bammmm, chime was back and fuller sounding than the GE, much better to my ears.   

Next, 15" WGS speaker.

Then I'll play with the -FB loop series R.

Then, since I'm still not liking the TS, I think I'll play around with that to.

I'm starting to really like this amp.


                  Brad        

[Ed_Chambley]

Ok, I put in the Ken-Rad NOS 5V4G and the Phillips JAN NOS 6L6GB set and biased them up to 44.1mA each., ~60%.

Wall voltage ~123.5acv;

Ken-Rad NOS 5V4G; pin 8; 420dcv

biased at 44.1mA, each, (the bias/balance works great, very easy to get within 0.2mA's between the pair and I really like the tip jack set up.)

Phillips JAN NOS 6L6GB; pin 3 (plate); 394dcv, pin 4 (screen); 394.5dcv
                                    pin 3 (plate); 395.4dcv, pin 4 (screen); 394.2dcv

Sovtek 5V4; pin 8; 420dcv (got this tube from Doug and it's right on the $$ for rectified dcv compared to the NOS.)

I think I might like the EH 6L6GC's a little better, a little cleaner and firmer. I have a set of -C- 6L6GC's that I bought several years ago, I'll try those too.

Big surprise, when I put in the JAN/Phillips 6L6GB's I put the NOS 12AX7 GE into the 1st preamp position and the new Tung-Sol into the TS CF position and although the GE still sounded better to me than the NOS 12AY7, more chime, it lost some chime and fullness. Flipped/flopped the 2 and bammmm, chime was back and fuller sounding than the GE, much better to my ears.   

Next, 15" WGS speaker.

Then I'll play with the -FB loop series R.

Then, since I'm still not liking the TS, I think I'll play around with that to.

I'm starting to really like this amp.


                  Brad        

Glad it is coming around.  I like the Gibson amps I have played.  Yes, a tad of difference using the 6L6.

[Willabe]

Glad it is coming around.

Thanks Ed.     Took me long enough to get after it and finish it.   

Yes, a tad of difference using the 6L6.

Yeah, your not kiddin!   

Been at least 15 years, probably closer to 20 since I wrestled with something this big on stage in a club. It's got some muscle compared to my little 6V6 amps.   I think it would sound great with a band in a room that could handle it.     

Gibson catalogue says "25w, with reserves to 35w." It's every bit of 35w! It would be fine playing in a club/bar with the volume set around 5 to 6 ~ish, still pretty clean with the guitars volume rolled back for rhythm parts . (With the 12AU7 PI you can/need to get it up a little bit more than if it had a 12AT7 or 12AX7 PI. Otherwise probably be set on 4.5 to 5 would sound about the same?)

I need to plug in my LP with HB PUPS and see how it likes that.

I'm running out a gas here, let's see if I can get that 15" wired up in it's cab tonight.

                         
                                        Brad     

[DummyLoad]

some suggestions... and bode plots.


--pete

[DummyLoad]

cont'd...


--pete

[DummyLoad]

last...


--pete

[DummyLoad]

some tweaks in the posts prior, but still nothing to write home about.


IMO, graft in the 5F6A TMB or the AB763 TMB and use the switch for mid boost: the front panel can be changed.


as i stated earlier: i recall that the stock TS sucked so bad that i compromised and built what i linked to previous.


just my 2cents...


--pete

[Willabe]

Ok, put the WGS 15" alnico and it sounds real good to me.        Very nice bottom end, very nice top end without being harsh, and ~more scooped in the mid range than the Tubby Tone alnico hemp cone.

Tone Quest Report mag raved about this 15" for a Jensen alnico type, and so far I'm not disapointed. It should sound better as it breaks in. The mid boost can easily add back all I need, and then some, if I want it.           

as i stated earlier: i recall that the stock TS sucked so bad that i compromised and built what i linked to previous..

Yes, I don't like it!      Dag nabit, do what I tell you to do when I turn you!          

IMO, graft in the 5F6A TMB or the AB763 TMB and use the switch for mid boost: the front panel can be changed.

Yep, I think that's what I'm going to do.

just my 2cents... .

Worth a lot to me Pete, thank you!       You have repaired, bread boarded and built a LOT of amps and I trust your experience and ear very much! At this point, I'd say you know your way around a TS.   

I can definitely hear some to quite a bit of the Rory Gallagher Irish Tour tone coming from this amp with my rosewood fret board strat, and a bit more now with the WGS 15". I'm liking this amp more and more.

I only found out after I started this build that his tweed tone was from a 5E6/5E6A Bassman, which this Gibby amp is closer too and NOT a 5F6/5F6A. (Although......        I think he might have been using a Treble boost pedal in the front? He used 1 with his AC30 in his 1st band, Taste.)

Next, -FB series R, then the TS.     


                    Brad   

[SILVERGUN]

Hey man, this is good reading....

It's cool to watch you get it to where you want it, instead of just settling for where it was.

Keep reporting!
 

[Willabe]

All right, I just took out the 100K -FB series R and tacked in a Dale 33.2K I had and now I can really tell when I rotate the presence control, really makes a change now.   

Sluckey, I went that small (33.2K) to add enough -FB to make sure the OT isn't wired up backwards. I thinks it's correct.   

I'm going to try tacking in a 100K pot and play with that.

The 33.2K might be a little much with the presence all the way off, but, when I add some presence, even full up, it seems like the low E string stays cleaner. I like that, a lot!

I'm also surprised that I like adding some presence with this amp. Even full up it sounds good to me for some things.

The WGS 15" alnico sounds very good to me with this amp. (Haven't tried it with another amp yet.) Although the Tubby Tone 12" alnico hemp cone sounded very good too. Now that I added the extra -FB I'll have to try it again.

The extra -FB seems to have tamed the volume a little bit and for me, that's a good thing.

I took out the NOS GE 12AX7 and put in a 2nd re-issue Tung-Sol 12AX7 and it sounds better to me, a little rounder/warmer and a little more chime and a little more sustain.

I was getting very worried, by the way it sounded at 1st, that I built an amp I was not going to like.

But, I REALLY am liking it now!!!!!! This thing sounds killer!!!!!!        I would LOVE to have a gig to put this thing through a full night with a band!!!!!!!!  (I've been playing at 5/12:00, on the bright channel volume.)

I am very glad, now,    that I built it. I am NOT disappointed at all.

I still need to play slide, tuned up to open E with my LP with HB's, I'm betting right now it's gonna sound great!

Still gonna try a different TS and try some different brands of power tubes I have. 


                        Brad         

[Willabe]

I dug through my box of power tubes I have stashed and found;

SED -C- SV6L6GC
NOS PhilipsEGC 7581A
GT-6L6GE-D
GT-6L6S-D
Sovtek 5881

I have a couple of sets of NOS PhilipsEGC 7027A's (6L6GC type) but because of their pin out, I'd have to lift the screen R off of pin 6 on the tube socket. Might be worth it to hear them?


                   Brad   

[Willabe]

Well, between our little beagle, Emma, who can't stand the noise and just seeing me walk by with my guitar, she jumps up and runs, (our golden Rory, she doesn't seem to mind it much) and the neighbors, I've been a little afraid to spend the time turning this amp up to test it while playing through it.        

But I did get a chance tonight to put in the SED -C- 6L6GC's. I set them for 70%, which worked out to be ~53mA's each, at 396dcv on the plates.

Sounded good with the strat, bright channel, volume on 5, but at that bias the low end was distorting a little much for my taste, when I did a simple low end open run descending to open E. I can lessen it quite a bit by picking closer to the bridge as I descend to the open E. (I've been doing that for a long time and it works well, but still, a little to much for me.)

Then I tried my Heritage Les Paul (1st year they made them, early 80's) with Gibson reissue 58 HB's (? same 1's Ed has talked about) tuned to open E with a Mudslide (black ceramic) and a heavy weight/thick wall glass slide.

Meh! No good!        I was very surprised and disappointed. It wasn't harsh or thin/piercing sounding (and I play slide with my fingers, not with a pick) but it did not soar with sustain, like slide should. I consider electric slide fretless guitar, like a violin. That's what the string bending blues players were trying to do, make it sing, with sustain and finger vibrato like a violin.   

And when I tried to turn up the amp past 5 the top 3 strings fattened up but the bottom were just mud! Meh! (I play mostly single string slide with some double stops, I don't play 4, 5, 6 strings at a time.) Even tried turning up the mid boost, no help, even full up. Then I tried the Tone Tubby 12"alinco, hemp cone, which has more mid range then the WGS 15" alnico, Meh, No help! 

My little 5G9, for me, just kills for my style of slide. I love it!     

(I didn't try tuning the Heritage LP back to standard tuning and playing regular guitar with a pick. I'll try that soon.)

So, I think I'll try a 12AT7 in the PI for slide? Might help?

Try more tomorrow and report back then.


                      Brad            

[SILVERGUN]

Sounds like you need MORE GAIN!!   

Let's see....
If you parallel V1 and add another socket you can ................
 


As you're talking about low note distortion, and, at times mud,,,,I can't help but think about lowering the values of your cathode bypass caps...
Without reading back through, I'm not sure if you addressed that yet. 

[Willabe]

Sounds like you need MORE GAIN!!   

Let's see....
If you parallel V1 and add another socket you can ................
 

 

As you're talking about low note distortion, and, at times mud,,,, I can't help but think about lowering the values of your cathode bypass caps...

Good call. I did use a 10uF for the bright channels V1 and I also used a 10uF for V2a CF driver.

I'll order some smaller by pass caps from Doug and see if that helps.


             Brad   

[Willabe]

Sounds like you need MORE GAIN!!   

Let's see....
If you parallel V1 and add another socket you can ................
 

Hey wait a minute.        

I could try using a jumper cord to bridge the 2 channels like with a Marshall 4X input jack set up.   



                   Brad