Blues Custom Mods

[PapaMidnite]

Be VERY careful Danny.A Shock Can KILL .Also very addictive once you start . But seriously If you have not done anything like this before .Please read up on discharging your amp

[Dannyboyee82]

Well, I did it.. C6 and C5. Luckily I already knew about discharging my amp Papa, but thanks for the heads up!

 

My opinion is that it has made the amp way too dark, I don't find the EQ more tweak-able at all, in fact it has limited the range of the EQ significantly. Playing a humbucker guitar such as I do, with the neck pickup now sounds awful. I'm going to replace the caps this weekend.. does anyone know the value of the C5/6 caps?

[jefrs]

Try putting C5 and C6 back down and shunting the 1Meg R5 and R6 with an 820k in parallel to each (R5 and R6 become 450k) and the fundamental pass frequency is halved, also the potential divider is halved (more signal to next stage), the sound opens up with increased bass but no loss of top end, not dark and not harsh.

 

There are problems with the TMB tone controls, it is trying to be too many things at once: read my 18 April notes above, it can be fixed.

 

Have we mentioned that changing the 5AR4 valve helps it a lot?

[mjlewis22]

Hi all. I'm new to this forum, tube amps...I'm pretty much green all over.

 

I recently acquired a BC30 as restitution for a bad purchase I made of a counterfeit Les Paul...and thats another story in and of itself. I was skeptical, I knew most of the things to look for, I called G.C.S. twice to authenticate the serial number and still got fooled. Anyway I explained what happened to the nice gentleman and he took the guitar back and gave me the amp and some other things to make it right.

 

I was gonna just sell the amp but I couldnt resist the urge to plug it up and give it the old college try and...well I really like it. Overall, I think the tone is much better than my Peavey VK--of course this amp doesnt have nearly the gain that the VK does.

 

My main axe is a Tele and I've discovered the brightness issues that most of this thread deals with. I normally play through Ch2, as I dont have a lot of use for clean stuff. (I play the alt-country/rockabilly D.B.T and Lucero style)

 

As I understand it, and I dont really understand it at all, but I can read, doing the cap-mods sort of kills the overdrive, and if anything, I need more...oomph...as opposed to less. After multiple reads and extensive contemplation over this thread, I have the following questions:

 

1) What is the best way to "fatten up the sound" and at the same time add a little bit more overdrive?

2) Where can I get the parts needed to do the Master Volume mod? Is there a post-phase inverter MV mod for this amp?

3) Is there a manual for this amp?

4) For under $50--which tubes should I change?

 

If someone would be willing to walk me through these mods a little bit I would photograph/document it for other users.

 

Thanks in advance. I really like this amp and I have enjoyed reading this thread as I have already learned a great deal.

[Dannyboyee82]

1) What is the best way to "fatten up the sound" and at the same time add a little bit more overdrive?

2) Where can I get the parts needed to do the Master Volume mod? Is there a post-phase inverter MV mod for this amp?

3) Is there a manual for this amp?

4) For under $50--which tubes should I change?

 

Hi there..

 

I have just modded my BC 30 with a master volume mod, let me tell you.. it is exactly what this amp needs.

 

In answer to your questions..

 

1 - Buy some DECENT tubes, there is NO POINT putting in substandard tubes.. I would recommend Svetlana Winged C's for output, Sovtek 5AR4 for Rectifier, JJ ECC83 for Pre-amp and Reverb.. leave in the EHX 12AX7 for PI. If you're still not happy, try swapping the speakers for different ones. I'm going to put some Greenbacks in mine soon.

2 - Not sure about where you would buy the parts from in the States, I'm from the UK, but there is a post PI master volume mod - you need to swap out R39 for a 1 meg variable resistor with the pot fixed to the chassis. With the new pot wide open your amp will be as it was before the mod, but now you can control preamp gain with channel 1 volume and control the output volume with the new 'master volume'. It works really, really well.

3 - You should have got the manual when you bought it? It isn't very good, it has very few basic details. If you are after a schematic, PM me.

4 - I answered this with question 1, THERE IS NO POINT replacing the tubes in there already for cheap ones.. you will need to spend a bit if you want to see results. I don't know how much you pay for tubes over there, but in the UK I spent around £70 replacing mine.. about $110 in your money.

 

Hope this helps.

[mjlewis22]

Thanks for the reply.

 

Just before I get started with this, I've recorded something on the stock amp Class A, EQ ind., using an SM-58 1" from the grill off-axis and a stock Mexi-Strat, neck/middle pickup, volume 8, neck tone 6, bridge tone 3

 

The temperature in the room was 74º and the air conditioner was off. :) Never mind my playing, thats not whats being studied.

 

Here is a pic of the panel:

 

 

And the recording (volume is low)

 

http://www.cae.tntech.edu/~mjlewis22/bc30mods/little_wing_bc30.mp3

 

Linear or audio taper? Shielded Cable? Which leg goes to what? Should I use the standby switch hole? What physical dimensions are needed to fit and accomodate a chicken head knob?

 

Thanks again...as soon as I am able I will get some new tubes...and as soon as I figure this out some more I'll try to do the MV mod and take some pictures and what not.

[mjlewis22]

Well,

 

I decided to give it a go. I stopped by Radio Shizzle and got a 1M Pot with a really long stem--guess I'll cut that later. As seen in the photo, it measured out at ~850 kΩ. Dont pay any attn. to that bottle of Dickel.

 

 

So I put the Beastly30 up on the table and tried to take the back off of it. I never could get it completely out, but I got it out enough to fold it down.

 

Next, I didnt know what to do. I went and got my winter gloves out of my drawer and put those on and tried to remove the power tubes. I decided I couldnt do that w/o breaking something so I just quit and went ahead and loosened the...amp...from the cab.

 

 

After removing the amplifier I gently sat the transformers down on some notepads and snapped some photos. The reason I stopped here is twofold:

 

 

1) I dont know how to discharge the capacitors, and I dont know where to put leads to check voltage across them. If someone could look at this picture and explain that I'd be very grateful.

 

 

2) I'm not really sure how to proceed. First of all, once I unplug the spade terminals from the standby switch how do I reconnect everything? SS1 to PT1 and SS2 to PT2? Second of all...which leg of the 1M pot connects to what side of R39?

 

See photos:

 

Standby switch:

 

 

Resistors: (R39 is dead center in the photo.)

 

 

Being thoroughly perplexed and ever so slightly afraid, I just covered it up and left a nice note for the roomies.

 

 

Any help would be well...imperative.

 

Thanks.

[Dannyboyee82]

Hey Mj..

 

The time difference is obviously the reason why I have not replied.. it is now 8:30am here and I'm about to leave for work.

 

Firstly, for some reason I cannot view your photos or listen to your recording. It says that the page is unavailable or whatever.

 

Secondly, you don't need to remove the stand by switch to accomplish the mod. I assume you have been reading the post by another forum member Jefrs? He wanted to get rid of the stand by switch anyway, I would recommend keeping the standby in.. although the argument for and against the standby on this amp is open for debate, at least you can have the option by leaving it in. If you don't want to use the standby switch, just leave it in 'play' mode permanently. You should mount the master volume pot on the chassis by drilling a hole for it.

 

If, like me, you have limited knowledge of working inside amps, you should take it to an amp tech. I know that to do this job you need to remove the printed circuit from the chassis and this process involves de-soldering various components. This was not a job I would have wanted to do myself, so I took mine to a guy that builds and repairs amps. He charged me £5 ($8) for components and then his hourly rate on top.. included in the bill for components were a load of replacement resistors and capacitors for the reverb stage (a whole other story).

 

What I can do, when I get chance, is to open mine up and send you some photos of the mod.. if you're feeling brave enough!

[mjlewis22]

Danny...thanks again for the reply.

 

If you'll notice I fixed my earlier posts to make everything happy and visible. I had to drop by the office to use the server there, which I am supposed to be able to login to from home, but I cant. On that note...does anyone know where you can get some free server space to hold pictures and what not?

 

Anyway, I'm thinking I can take a look at the schematic to find the resistor adjacent to the + side of the large caps and just clip that to ground to drain them...I'll be wearing thick gloves just in case.

 

As far as the standby switch goes, I think I'm just gonna leave that where its at for the time being.

 

The only issue I have left is wiring up the 1M pot. I was looking at it last night, and nearly as I can tell the center lug is common to the other two lugs, and it just divides the signal between them. I think what I will do is turn it all the way clockwise and connect the two that are shorted together where R39 was with a two conductor cable. Then I'll just fold over the other lug and solder it to the case and solder the shield to the case and solder the other end of the shield somewhere else, that way whatever signal is not being used just gets diverted to ground...or is that even necessary?

 

Finally, should I leave R39 in there? B/C if you turn the MV pot all the way up and there used to be a resistor there what happens?

 

So anyway I'm gonna drain the caps when I get home and wait on a response I guess.

 

Thanks,

 

--ML

[Dannyboyee82]

Hey Mj,

 

Ok.. this morning I had chance to take a look inside and get some snaps of what my amp tech has done. You can see that the pot itself is a variable resistor and I have given you close ups of where you need to wire it up. It is shielded wire, and I assume it will be a linear pot. If you can handle getting beneath the PCB (I'm a little ham fisted when it comes to things like this, I can wire up a guitar.. but this is a little too intricate for me!), then have a go.. these photos should give you a good idea of how to go about it.

 

 

 

 

 

 

 

 

Your recording sounds good, the only thing I would do differently is the EQ, I spent a few months playing this amp with the bass maxed as you are.. but now I have it around 2 o'clock for both strat style and humbucker guitars. I'd have the treble around 10 o'clock (strat) or 2 o'clock (humbucks) and mids between 12 and 2 o'clock for both strat and humbucks.. this is on class A or A/B and with the interactive EQ. Oh, and for the drive channel I have the second mid control around 2 o'clock, that seems to balance the two channels out. At higher volumes you will find you need to back off the bass from here and maybe push up the mids a little.. it gets too woofy in a band situation.

 

With the MV mod, you can get some nice tube saturation at bedroom volume and even some harmonic overlays. I'm about to test it out for real tonight though, we have band rehearsal tonight.. I shall report back with my results of what it sounds like cranked.

 

With a little tweaking this amp is really, really nice. It takes pedals really well, I use a Big Muff Tone Wicker most of the time.. with a cranked amp, that thing sounds sweet. I have just ordered a HBE Germania from PGS as well.

 

Hope this is helpful.

 

Danny

[Dannyboyee82]

Oh.. one more thing.. if you want to hear what my amp sounds like (before the MV mod at least) go here http://www.myspace.com/operationkinomusic

 

That is my band.. I'm the only guitarist, the BC 30 volume was cranked to about 2-3 o'clock with the EQ settings I mentioned in last post and on class A/B with Clean channel, I'm playing a Strat apart from on 'Hold My Breath' which I used an Explorer.. no pedals (the Big Muff was too noisy to record) so all you are hearing is the tube saturation. The tubes are..

 

Output: 2 x Svetlana Winged C

V1 and 2: JJ ECC83S

V3,4,5: EHX 12AX7 (stock)

Rectifier: Sovtek 5AR4

[mjlewis22]

Ok, I think I get it.

 

By connecting the center lug and side lug, the total resistance across the pot changes as you turn the knob. One side of R39 is already connected to ground, so there is no need to ground the pot.

 

It's been sitting for two days so it should be good to go...I'm gonna give it a try when I get home from work today.

 

--ML

 

BTW, I enjoyed your recordings. Your tone, and your band, sound great.

[Dannyboyee82]

Just to let you know, the amp now sounds like a beast with the MV mod. I had it cranked last night and wow, what a difference.. driving that preamp certainly makes this amp come alive.

[mjlewis22]

I finally did the MV mod. It works very well, except that when you turn the knob CCW it gets louder. I put the new knob on the back of the chassis next to the output jacks.

 

Even with the volume tamed, I was having some problems with harshness still...I just felt like I couldnt get the EQ quite dialed in for the sound I was after. I decided to give the Marshall 20W mod a try.

 

I went to the technician in the EE dept and asked him where I might find a couple 470k/1W resistors. He said "Whats this for?" and I said (and I dont really know what I'm talking about) "Cathode bypass resistor...to fix some harshness..."--trying to regurgitate what jefrs said about that mod--and he said,

 

"Yeah 1M is pretty big right there. Try these 5751s and see if that dont fix it."

 

GE 5751s in V1 and V2. That fixed it. Instead of screeching, it sings. I was blown away by the sound of this amp with the 5751s...when you max them out with the MV down you get this very musical overdrive thats absolutely creamy and beautiful.

 

I'm still gonna give the Marshall 20W mod a try, and I'm gonna put the resistors on a toggle switch, but let me say that changing those 12ax7s to 5751s made a HUGE improvement.

 

--ML

[Dannyboyee82]

A 5751 is a low gain alternative to a 12AX7/ECC83.. it probably would tame your amp a little and make it a bit smoother. They're pretty expensive pre amp valves you have there.. if it works for you then why not. Glad your MV mod worked out ok.

[mjlewis22]

I switched out R5 and R6 for 470k. I was gonna put them on a switch but I couldnt figure out how to switch them both with the 1 DPDT I had available.

 

It's hard to say how much it did for the tone...maybe needs some EQ tweaking now, but it definitely opened up the overdrive a bit. Before, I pretty much had the drive maxed out for most songs and now I have a little headroom, so I'd say it was a good change.

 

 

Anybody know anything about a footswitch for this?

 

--ML

[Guitarnut]

Also you must realise the the big filter caps can and will hold enough charge to kill you, so before starting work simply use a wire with insulated crockodile clips to short the anode/plate resistor of valve1 (the one nearest the instrument input) to the chasis. Within a couple of minutes the resistors in the amp will have drained the filter caps.

 

I know it's been along time since this post but I'm in need of some clarification on this. I want to discharge my BC30 in order to do the MV mod but I need to be sure I'm discharging properly.

 

So the R that Andyroid is referring to would be R4 coming off of pin 1? ...see attachment. Once the above step has been taken, how can I verify that the caps are indeed drained? Meter from the + side of the cap to ground?

 

 

Thanks,

Mark

[jefrs]

I would be disinclined to use a pre-amp valve anode resistor such as R4 as a discharge route because they generally do not have sufficient power rating.

 

Find the anode of one of the output valves and discharge from there, through the transformer primary. The cap connections are inaccessible but the valve base connections are easily got at, especially if you think the circuit may be hot. Do remove the mains lead, my favourite, ouch!

 

This may not be necessary since the BC30 does discharge itself, but it is nice to check with the voltmeter before plugging yourself in.

[jefrs]

Hi all. I'm new to this forum, tube amps...I'm pretty much green all over.

 

I recently acquired a BC30 as restitution for a bad purchase I made of a counterfeit Les Paul...and thats another story in and of itself. I was skeptical, I knew most of the things to look for, I called G.C.S. twice to authenticate the serial number and still got fooled. Anyway I explained what happened to the nice gentleman and he took the guitar back and gave me the amp and some other things to make it right.

 

I was gonna just sell the amp but I couldnt resist the urge to plug it up and give it the old college try and...well I really like it. Overall, I think the tone is much better than my Peavey VK--of course this amp doesnt have nearly the gain that the VK does.

 

My main axe is a Tele and I've discovered the brightness issues that most of this thread deals with. I normally play through Ch2, as I dont have a lot of use for clean stuff. (I play the alt-country/rockabilly D.B.T and Lucero style)

 

As I understand it, and I dont really understand it at all, but I can read, doing the cap-mods sort of kills the overdrive, and if anything, I need more...oomph...as opposed to less. After multiple reads and extensive contemplation over this thread, I have the following questions:

 

1) What is the best way to "fatten up the sound" and at the same time add a little bit more overdrive?

2) Where can I get the parts needed to do the Master Volume mod? Is there a post-phase inverter MV mod for this amp?

3) Is there a manual for this amp?

4) For under $50--which tubes should I change?

 

If someone would be willing to walk me through these mods a little bit I would photograph/document it for other users.

 

Thanks in advance. I really like this amp and I have enjoyed reading this thread as I have already learned a great deal.

Hi,

1) the thing I mentioned about putting a jumper across the 1Meg resistors does "open up" the sound on both channels, you still get the top end but more mid and bass, the amp seems to breathe more easily. I also posted a mod to the cathode resistor of V1B the CH2, I added this when I removed the bright switch mod from CH2. This does change the gain and fatten it up on CH2.

2) the MV mod to R39 that I posted uses a knurled Alpha 250k VR and some shielded wire like you might use for a humbucker. This is before the phase inverter. If you want a post-PI like a Marshall then you would need a dual-gang pot and to research Marshall amps.

3) There is a (cough) manual for the BC30, you can get the circuit diagram of the interweb.

4) if there is one valve that is must-change, then it is the chinese rectifier, I got a Sovtek 5AR4. The Sovtek 6L6WXT+ bottles are actually not too bad at all, and the EH12AX7 could be worse.

 

I think the first mod I did to it was change the speakers, because it was so hard and harsh I fitted Celestion Classic G12M-25 Greenbacks. The original Eminence pot-luck types sounded something like Vintage-30, which are fine at high volume in a closed cab but otherwise very harsh and nasty. Better but even so, this did not fix its problems to my liking.

 

I keep meaning to open the amp up and check my mods that I've put in and removed and put in again, my notes I'm afraid are a bit of a mess.

From memory:-

Speakers

Rectifier

Re-valve

Bright caps, switches V1A CH1 V1B CH2

Fat gain V1B CH2 (no bright on CH2)

MV R39

Tone control (several false starts)

Shunting the 1M pair of resistors on CR-filter to drop frequency

And Castors!

I think I found a single CR that I also shunted but I cannot remember which one but that it made the most significant difference.

I need to do this and post the "final" mod details...

[jefrs]

Ok, I am posting my mods circuit diagram, recently updated and corrected. It's quite large so I don't know how long I can keep it on here...

Click on the thumbnail to enlarge. It's about as big as anything we can post on here, I hope you can read it.

[mjlewis22]

Thanks jefrs.

 

...you've got me wanting to crack it back open again...

[jefrs]

re the post above here's a run down of the modifications. I may have incorrectly stated these earlier: my eyesight is not good on small print and was working from memory. I have now updated that diagram from the circuit board and refreshed my notes... so hopefully...

 

Connect fan to heater circuit (it was open circuit from new)

Remove self-destruct switch (standby) and use hole for Master Volume

Tidy all wiring, see diagram notes

Re-valve, rectifier replacement is a must-do as the chinese Electron-Tube 5AR4 is noisy, spitty, rubbish. Other valves see previous posts and discussions

 

Actual modifications, note I have undone some of the first ones e.g. part of the tone stack mods, and C16 reverts to stock - - - >

 

Bright caps C4 on bright switch DPDT, C6 lifted (not used)

 

820k Shunt on both R5 and R6 to "open up" tone and allow amp to "breathe" (higher signal level through lower R)

On other half of bright switch a switchable 6k8 shunt across 10k R15 making 4k when on, to give "fat" gain at V2A. Note this fat gain switch is on V2A CH2, not V1B as previous stated.

 

CH2 mid control R14 replaced with 100nF poly cap, changes mid frequency (keep removed 223)

 

Tone stack slope resistor R22 replaced with 33k (note C16 reverts to 471. previous mods undone).

 

Tone stack additional cap 223 inserted between C18/VR6 and VR7/R23, this gives a more conventional tone control whilst allowing the interactive/independent function.

 

Do note I have shown actual factory values of pots etc in green where these are different to those shown on the standard circuit diagram.

 

Master volume Linear B250k (Alpha) potentiometer (no, not variable resistor) replaces R39 with wiper onto lifted leg of C27 before phase inverter. Shielded cable grounded one end only on PCB.

 

Other modifications

2-off Celestion Classic G12M-25 speakers 8ohm with series/parallel switch (as per Marshall cab)from stock it's a harsh amp, ymmv.

Castors, no-brainer!

Tilt-back legs (Long Fender), it should be obvious that this is a very loud directional amp. If the player stands over it they cannot hear its volume and will play too loud, drowning out the entire band: tip it back!

[jefrs]

One other thing I did was take the PCB out. This is quite tricky and, yes, I managed to drop the chassis in the process. I lost the input jack corner and VR2. VR2 was easy to replace with a standard PCB mount pot. I had to Dremel off the corner of the PCB complete with the input jack and replace the jack chassis mounted, and re-build the input circuit PTP and route the wiring around it. Strangely this also cured some of the mains hum because the BC30 is grounded all over the place to the chassis.

 

Lesson: the BC30 PCB is quite thin and fragile - don't take it out unless you must.

[mjlewis22]

FYI

 

Pictures of the MV mod on the Gain Stages thread.

[PapaMidnite]

Well well look at this thread it has grown a bit .Nice work all of you. Keep on with it and post some sound bits if you can I would love to hear some .I will pass along to the designer Pytor he will get a kick out of this one.