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Hi, i'm new on this forum!

I'm from Italy. I've got a beauty Custom Blues 30, version with stock 6l6wxt+. After the C3, C5 and C6 mods (i totaly removed the caps) i have got a big sound improvement on the bass side but also a big noise like "POP" every time that i switch between clean and overdrive channel. Wath's happen? Can you help me?

Please help me!!!!

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Thought I'd keep this thread going. Recently picked up a rebadged socal (Grainger Hammerhead) and cab for a stupidly low price and saw all these socal / bc30 mods. However, I couldn't resist going the whole hog so I modded the pcb into a 50w splawn quickrod clone. The total mod cost including the footswitch was $75. I decided to keep it "fx loop"-less and I added a swell control to the reverb as well. It sounds great, even with the stock speakers.post-61782-004551500 1387029543_thumb.jpgpost-61782-002649600 1387029550_thumb.jpgpost-61782-020370900 1387029557_thumb.jpg

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Hello,

my name is Sven. I tryed the mod cut C5, C6 and R15 to 1,5 K. On Channel 2 I have just a little bit distortion? The clean channel ist good.

 

I want more distortion. What can I do?

 

Sven

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I've just found another design flaw that may be the sole reason the BC30 self destructs. There is not enough limiting resistance before the rectifier. Limiting resistance helps keep ripple current within limits and is stated on the datasheet.

 

14054956103_ee737e8325_o_d.gif

 

It is worth noting that the choke will slightly lower the required limiting resistance, but not by much. The above datasheet chart provides the calculation necessary to determine the limiting resistance provided by the transformer:

 

Rs = Rsec + N2Rpri

 

I have measured Rpri to be 5.5R and Rsec to be 37.5R (75R for the entire winding) so...

 

Transformer ratio N = 350 / 240 = 1.45 so...

 

37.5 + (1.45 * 1.45 * 5.5) = 49R

 

The chart shows that for a 350V tap, the limiting resistance needs to be around 105R for EACH PLATE of the rectifier, and this is for a fresh valve manufactured to 1959 standards. So lets assume 115R will be safer for modern 5AR4s,

 

115R - 49R = 66R

 

68R is the nearest standard resistor, two of these should be chassis mounted inside the amp, and the transformer secondary taps (350V) should be wired directly to these and then the other ends of the resistors wired to the PCB. I recommend 25W types, as the voltage rating should be in the region of 550V. The working voltage in practice will be much much lower than this but at the moment of power on, it will be higher and it's nice to know that nothing can go wrong! I over spec almost everything in my amps!

 

BTW, using the standby switch makes the problem worse because the rectifier is fully ready to conduct. If you are unlucky enough to flip the switch at the moment the mains AC voltage is at it's peak then destruction is almost guaranteed. Starting the amp from cold (without the standby) will slightly reduce the likelihood of failure. So, for a happy BC30, don't use the standby and install limiting resistors!

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Hi all,

Old thred but;

I have been running KT-66's in my bc30 since 2011 and no problems.

no mods, it made the sound fuller like it could breath better.

It still can kill with single coils through.

Now on to mods , I have looked at the 50 cal schm. And r5 is 1m but r6 is the 470k. I am going to make a 470 for r6 and see whats up.

I have owned it from new love this beast.

My question is about the PT and the resistors that need to be installed? What and were please?

thanks

ps,never seen so many cold soilder joints in my life. If I knew before I would have fixed it!

 

Follow up, I found some info on the rec being screwed up by start up ripple and cathode death..

Should the resistor go across the "Dumb #ss switch" IE stand by switch so it always has slow leak??

I know never use the stand by Switch but doing a cold start so the rectifier builds up slower? Or would a Cap be a good addition to the resistor?

 

Time to get P spice running a sim. of this..

 

Also, the idea of putting a heater SW in with a diode so it will cut heater v by 1/2

 

 

Too the guys that say you can't run KT-66 tubes The guy who made the BC30 said it could handle the 66's plus

the ot is 22k ohms and the KT-66 are rated at ahhhh 22k ohms. Sounds like it might work...

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Hi, my previous post may be a little difficult to read, I've never been good at writing. So, I'll show you two schematics, the original, then the modded one. The first one shows the original power supply. The transformer secondaries (350-0-350) go to the 'Standby' switch and then to the main circuit board. These are relatively thin red wires that come from the power transformer, through a rubber grommet in the chassis and then go directly to the 'Standby' switch.

 

14299937322_9d303e5cb4_o.gif

 

The next schematic includes the two new 68R resistors, the green arrows point to them.

 

14278732876_aae5287642_o.gif

 

There is plenty of free space on the end of the chassis to bolt on the new resistors. This is probably the trickiest part of the mod if you want it to look tidy, as you obviously have to drill from the outside, but the resistors go in the inside. The important thing is that the mounting holes are the correct distance apart and that it is electrically safe. I sort of eyeballed it and used the resistors as a guide to get the holes the right distance from each other. If you see what I mean...

 

On to the wiring. All soldered connections should be covered with heat shrink, simply slide an appropriate length of heat shrink down the wire before soldering, then you can slide it back over the finished solder joint when you are done.

 

I recommend cutting these secondary (350-0-350) wires and inch or so from the standby switch (to allow easy joining of new wire). You now have two long (6 or 7 inches) of thin red wire coming from the power transformer. These will be tied to other wires to keep things tidy (you may find it easiest to cut the plastic cable ties to free things up). Strip some of the sleeve from the ends of these two and solder them to the new resistors. You then need two additional pieces of wire to go from the other ends of the resistors to the inch or so of wires hanging from the standby switch. Attach them accordingly and don't forget the heat shrink!

 

I find the best way to attach two lengths of wire is to twist and tin each of them, then bend them into hooks. Hook them together and squeeze them tight using pliers. Then solder them together properly, cover with heat shrink, and you're done!

 

 

 

Too the guys that say you can't run KT-66 tubes The guy who made the BC30 said it could handle the 66's plus

the ot is 22k ohms and the KT-66 are rated at ahhhh 22k ohms. Sounds like it might work...

 

 

In an amp like the BC30, KT66's actually want to see something like an 8k load. The BC30 transformer presents something like 4.4k. So simply plug you speakers into the 'next socket down'. On the back of the amp there are sockets for 4, 8 and 16 ohms. Relabel them to 8, 16 and 32 ohms and you wont go far wrong.

BTW I ripped the guts out of one of my BC30 amps and gave it a Selmer Treble and Bass preamp, Fender-ish reverb and a sort of SoCal power amp using KT66s. Sounds fecking awesome. Turn the Presence and Reverb down and it's a killer bass amp too! (Still building the head cabinet though, no bass combo should ever have valves in it!!)

 

Hope this lot helps!

Andy

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Super thread resurrection!!!

This thread has helped me a lot with my BC30!

Got hold of one about 6 months ago, first thing I did was swap out the sovtek output tubes which made a huge difference. All the 12ax7's are JJ's, so is rectifier.

Also have cut out c3 c5 c6 and added master volume on r39.

Have moved the fan power supply from the middle of the board to the place indicated on the schematic.

Amp sounds killer and it's now my main gigging amp.

Going to give the r15 mod a go, parallel a 5k resistor to the 2.2k to see what happens and then that'll probably be it!

Edited by Matttjuk

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Hi,

I'm new here, but read the complete thread thoroughly several times. I had the idea to summarize all suggestions and put them on github in a asciidoc project. People can contribute and modify the already available content. It would be nice if I could have a high resolution PDF from the modded scheme including the transformer output resistor mod.

In what application is the schema made in and is it available in it's original format?

I have the most important mods summarized in a text file, which I will convert into asciidoc so that it can be generated in a nice PDF.

Pictures of the mods made are welcome, they can be included in the project

I will put the project in github.

I have my BC30 for more than 5 years now. The first replacement was with Groove tubes (don't recall the exact type since labels fell off due to heat)

Now they were replaced by JJ Electronic's and the amp sounds harsh again and breaks up much much later in the drive channel.

I use the amp only for Neil Young tribute in the lead part, so I need a warm creamy overdrive that's gently saturated. The groove tubes did the job much much better. I play mainly on a Hagstrom Super Swede P90 tremar and as backup with a Yamaha AES-620HB with Seymour-Duncan HB in the bridge position. I put the amp in class A mode.

I also had a generic question about removing components. Is it possible to de-solder them without taking out the PCB completely?

Edited by geert peeters

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Another update as this thread has seems to have died 🤣

R21 is now 1.1k and C15 2.2uf, made a nice difference to the drive channel and the tone controls seem a lot more responsive.

So list of mods I've done are:

Master volume  (R39)

R15 now 1.5k

R21 now 1.1k

C15 now 2.2uf

C3, C5 and C6 removed

Standby switch deleted

Fan power moved from valve supply area to before the 5 diode's (V1 - V5)

That'll do I reckon, very happy how it sounds now.

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3 hours ago, Matttjuk said:

Another update as this thread has seems to have died 🤣

R21 is now 1.1k and C15 2.2uf, made a nice difference to the drive channel and the tone controls seem a lot more responsive.

So list of mods I've done are:

Master volume  (R39)

R15 now 1.5k

R21 now 1.1k

C15 now 2.2uf

C3, C5 and C6 removed

Standby switch deleted

Fan power moved from valve supply area to before the 5 diode's (V1 - V5)

That'll do I reckon, very happy how it sounds now.

 

 I'm in the middle of the mods. 
First round, I did the most rewarded combination of C3,C5,C6,R15,R21,C15 (according to my synthesis of this forum thread)
The amp has less highs now, but EQ is more controllable.
I need to try it out during the rehearsals tomorrow where it is cranked up and input signal boosted by my GT-5 pedal board.
I was planning to do the R39 mod, but I don't know which channels it impacts. If this allows to crank up the clean channel and controlling the master volume with it (potmeter), than this might produce an even rounder overdrive.
I'm working in the direction of the Fender 5E3 sound (which never will succeed completely). But this amp fits in my budget to use it for lead guitar in a Neil Young tribute band.

A side project will be the control of the pot meters with servo motors. My Boss GT-5 is a versatile and robust beast that has some nice MIDI features. Those midi messages will be taken in by an Arduino and this will control servo motors which will drive the potmeters.

This will allow me to tweak the sound from soft and harder rhythm parts to  a "full howling drive with delay" lead sound for solos.
I can use 5 patches and the express pedal to program whatever I want 😉

I'll just keep this posted here. It always can add more context to the splendid information already available here. 

BTW I always play in triode mode.

Edited by geert peeters

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The r39 mod is definitely worth while and quite simple to do. It effects both channels so you can crank both while retaining a bedroom level volume.

I've not noticed any tone difference with this mod so its win win. 

I run mine on triode too, I've not tried pentode with the new mods yet but got a band practice tonight so will give it a shakedown 

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I tried out the new mods in the band setup. C3, C5 and C6 together with C15 kills the dynamics totally

I play a guitar with P-90s 

The overall sound was overcompressed loosing bottom and high ends. 

It was like playing with a compressor on steroids. 

Neil Young's music requires control of the dynamics. 

I'm planning to put C3 and C6 caps back and definitely revert to the C15 22uF since the bottom end of my sound spectrum went on holiday

I'm just wondering which of the 3 brightness caps I best place back. I mainly play on the drive channel, so I guess most impact is expected from C5 and 6. Is that a correct assumption? Shall I start to put back C6?

Problem is I cannot test this at the fullest in my living room since dynamics of the amp change when level is cranked up. So an indication in advance might help to pick the right cap to put back

R39 replacement is next on the list and shortcutting the standby switch 

Edited by geert peeters

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On 4/27/2014 at 7:38 PM, Andyroid said:

I've just found another design flaw that may be the sole reason the BC30 self destructs. There is not enough limiting resistance before the rectifier. Limiting resistance helps keep ripple current within limits and is stated on the datasheet.

 

14054956103_ee737e8325_o_d.gif

 

It is worth noting that the choke will slightly lower the required limiting resistance, but not by much. The above datasheet chart provides the calculation necessary to determine the limiting resistance provided by the transformer:

 

Rs = Rsec + N2Rpri

 

I have measured Rpri to be 5.5R and Rsec to be 37.5R (75R for the entire winding) so...

 

Transformer ratio N = 350 / 240 = 1.45 so...

 

37.5 + (1.45 * 1.45 * 5.5) = 49R

 

The chart shows that for a 350V tap, the limiting resistance needs to be around 105R for EACH PLATE of the rectifier, and this is for a fresh valve manufactured to 1959 standards. So lets assume 115R will be safer for modern 5AR4s,

 

115R - 49R = 66R

 

68R is the nearest standard resistor, two of these should be chassis mounted inside the amp, and the transformer secondary taps (350V) should be wired directly to these and then the other ends of the resistors wired to the PCB. I recommend 25W types, as the voltage rating should be in the region of 550V. The working voltage in practice will be much much lower than this but at the moment of power on, it will be higher and it's nice to know that nothing can go wrong! I over spec almost everything in my amps!

 

BTW, using the standby switch makes the problem worse because the rectifier is fully ready to conduct. If you are unlucky enough to flip the switch at the moment the mains AC voltage is at it's peak then destruction is almost guaranteed. Starting the amp from cold (without the standby) will slightly reduce the likelihood of failure. So, for a happy BC30, don't use the standby and install limiting resistors!

 

I did some measurements by putting an ampere meter between de sockets of one of the fuses. I measured 63mA in triode mode. Playing guitar and driving a signal through the valves didn't influence the current.

Between the 2 coils I measured 670V RMS

If I'm not mistaken, the total dissipated power would be the square of 0.063A * 68 Ohm which is 0,27 Watt. I bought 2 resistors of 25W so I guess they'll do the job.

I hope that the drop of 4.29V caused by each resistor doesn't make a big difference for the characteristics of the valves.

Has someone tried this mod and what is the potential risk if I put those resistors in line? 

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