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OK forget the loop idea .Onto next Question. I would like to add a Bias pot adjustment. Looking at scheme where is Bias resistor located?I seem to be overlooking it.Too many late nights

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That amp is cathode biased, and simply adding a pot to R44 to screw around with extreme bias settings is just a bad idea all around when only adding 10 or 20 ohms can make a huge difference. Besides, R44 is a 250r/25watt resistor. Seen any 500r/25watt pots lately? If so, it's gonna be a bit large. And expensive! :-({|= And converting the amp to fixed bias, whether actually "fixed" with a resistor or variable with pot, is not an easy undertaking even for old guys much less new guys. Better work on your calculator chops before you tackle that mod. There's gonna be a whole lotta math and load lines involved. http://www.aikenamps.com/WhatIsBiasing.htm

 

Gil...

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Hi all, new to this forum.

 

I like the idea of C5-C6 mods. I have not really been happy with the sound of my BC30. Came with 5881's by the way.

A couple of days ago I pulled tubes from other equipment. I replaced the 2 preamp and the phase inverter with an RCA, a Mullard and a Telefunken all from very old equipment but test very good. Replaced the output tubes with Svetlana 6L6's used, 80%. It made a big difference in the sound. It is a different amp. Clean is very clean and overdrive is not near as muddy. But is still doesn't sound right to me. I am ready to start tweaking.

Steve

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I lifted C5 and C6. It does seem to be an improvement in sound. Was looking at the biasing of the preamp tubes. Just for fun I paralleled a 5k on top of the 2.2k R15 for approx 1.5k. Which slightly lowered the gain on that stage. The distortion is a bit smoother and not so harsh, well it it just sounded better to me.

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Yes it was 1 watt. Think I will keep the mod to R15, C5 and C6. Wish I could find a quieter fan though. When I bought the amp (used), the fan was not working. Bought a generic replacement fan and it is kind of loud. Never heard a BC with the stock fan so I don't know if it is normally loud or not. Let us know how it sounds without C10.

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stevecg2 Gave C10 a try ,sounds better I'll shake it out tonight at practice let you know .I didn't have a 5k laying around but i did try a 1k 1watt did the alligator clip thing on/off for testing I like the difference already. Really mellows out the drive channel ,Think I'm going to replace R15 with a 1.5k ohm 1 watt seems the drive is more manageable this way

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Oh yeah Stevie That did it. C5,C6,C10,R15 This amp is singin now Baby ,So much more manageable /tweak able [Tweakalishes] Tele is just lovin it ,I even Played My harps through it, Both clean and with the drive channels.I gotta toot our horns here We hit the jackpot=d> :-:D/

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Don't suppose anyone fancies doing a photo walk through on this - from opening the cab to reassembling? These would be fantastic as stickys.

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Hi all,

 

Thanks for this thread. I have used the suggestions to improve my own BC30. I play a strat with Fat 50s PUPs and found the clean channel insanely bright. I have done the following: removed C5 C6 and C3. I have also exchange R15 for a 1.6K. I did try removing C10 but found I lost way too much top end from channel two and replaced it. Before exchanging R15 My amp had a real 'snotty' midrange which was driving me crazy. It now sounds great. I would like to a slightly more fuller rounder sound though, any ideas? It is a much nicer sound now and very useable but I wonder if there is more sweet stuff to be had. The clean channel now is beautiful and I won't tinker with it anymore at this stage.

 

Cheers

Greg

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Nice , Another pioneir, Welcome ,I like the C3 also ,I replaced C10 as you did .As far as rounder sound I swapped tubes for more depth I chose Tung-Sol 5881 but for more drive Thd Yellow jackets with EL84's as far as pre amps go the jury's still out on that one ,Keep posting info Dave

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Ok here's a post from another site about EL34 tube swap idea I've been toying with .What do you think ??? An chanOK Tremo' date=' here's the amp specs, straight from Pyotr Belov:

 

Straight out of the Box BC30 with stock Sovtek 5881 - Line Voltage 120

 

Sovtek 5881 Plate 23W dissipation + Screen 3W dissipation.

 

B+ Voltage - 406VDC - Measured from Pin 3 to ground

 

Plate Voltage - 375VDC Measured from Plate to Cathode

 

Screen Voltage - 374 VDC Measured Pin 4 to Cathode

 

Cathode Voltage - 31VDC - Measured from Cathode to ground

 

Cathode Bias Resistor - 250 Ohm Rated 25W

 

Cathode Current - 62mA per tube

 

These specs were at idle.

 

I spoke with Pyotr on the phone tonight. He seemed to favor the 6L6GC for a replacement output tube, but he said that any 5881/6L6GC should be alright in this amp. While we were on the phone, Pyotr popped in a pair of EL34's and got these numbers: B+ 396v, Plate 367V,

28.5v Cathode voltage, 57mA per tube, Line Voltage 116v.

 

I'm going to run these numbers by Lord Valve to get his opinion....minus the 6550 recomendation that is...ce of op trans failure?or do you think it will handle it?[/quote']

 

Well, well....

 

Glad to see that you're still pursuing these BC 30 mods PapaMidnite (a.k.a. Tremo)!

 

The above quote is mine and it was directly from a phone conversation I had with Pyotr Belov in 2006. He popped the EL34's in the amp while we were on the phone and read off the specs. He seemed to think the EL34's would be fine with the circuit left stock, but I always wondered just how long they'd hold up without any circuit mods.

 

So, you just removed C5 and C6 from the circuit entirely and left those slots open? No bridge of any kind to the circuit board? That's pretty simple, and certainly welcomed if that's all it takes to tame the brightness.

 

I had gotten to the point where I was relatively happy with just the tube change to Tung Sol re-issue 5881's and 12AX7's. The tone did seem to mellow out after putting some hours on the amp. But... if this mod make the EQ more usable I have to try it....

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Not Tremo , But yes still plugging away at this .Update on BC is C3 ,C5,C6 put back C10 took too much top end away R15 from 22k to 1.5 K ;) I'm very happy here with this. Going to move on to other projects now .I've got a Dean Markley Cd 60 that has a bit of a hum problem .I'm also looking into the Egnator Rebel tube blending idea HMMMM . Update Markley solved. Power resisters NG. Not a bad find for free From transferstation 60Watt Two 6l6 Blonde Tolex amp:d/

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Not Tremo ' date=' But yes still plugging away at this .Update on BC is C3 ,C5,C6 put back C10 took too much top end away R15 from 22k to 1.5 K 8-[ I'm very happy here with this. Going to move on to other projects now .I've got a Dean Markley Cd 60 that has a bit of a hum problem .I'm also looking into the Egnator Rebel tube blending idea HMMMM . Update Markley solved. Power resisters NG. Not a bad find for free From transferstation 60Watt Two 6l6 Blonde Tolex amp:d/ [/quote']

 

Sorry, my mistake PapaMidnight. When I saw the quote and other references to previous info on the BC 30 topic, I made an assumption. And what's that saying aboutwhat happens when you assume something...?

 

I'm glad to see that those with the knowledge have turned it to the BC 30. It's always been a good amp, it's just needed of a few mods to tame the brightness.

 

Thanks for the clarification...

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I think this is what your looking for.http://www.ppwatt.com/files/ppwatt/E...VER01_DPPT.pdf

 

That'll get it.

 

Let's do this conservatively. Remove ONE cap' date=' then play and see if it's better (to your ears) or still needs less brightness. If it needs less, remove one more and then re-play. Etc.

 

First - remove C6.

 

Second - C5

 

Third - C10.

 

[/quote']

 

hi there, I had a go at this mod but only just C6. I haven't noticed much change in brightness but the Drive channel now sounds more like a fizzy distortion rather than a crunchy overdrive. Has anybody else found this?

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Definitly do the cap cut mod .It's amazing how much better it sounds .I got the idea after seeing and hearing it done to a Valve jr .I don't know why they make amps so bright these days
metal and "modern rock" (it isn't really rock in any sense... it's just a new name for un-shredded metal i guess...)

please excuse my language, but damn the 80's. i mean, there was some good music then, but shred and rap completely ruined modern music for me... and synthesizers...

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metal and "modern rock" (it isn't really rock in any sense... it's just a new name for un-shredded metal i guess...)

please excuse my language' date=' but damn the 80's. i mean, there was some good music then, but shred and rap completely ruined modern music for me... and synthesizers...[/quote'] Fen ??? What brought that on? Just felt like venting? I agree 80's had it's moments .Joe Jackson ,Elvis Costello,Talking heads just to name a few. But yes 80's had some good music

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G'day,

 

I have tried one further change which is to change R21 from 2.2k to 1k. Result is more gain and slightly fuller tone in my amp. Suggest using alligator clips a A-B test it. My next experiment will be to reduce C15 to 5uf or some value less. Problem is that to do that properly the PCB needs to be removed which will be a dog cause all the VR's are directly attached. Current config is C3,C5,C6 removed R15 now 1.6k and R21 now 1k

 

Cheers

Greg

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Hi, I'm urgently in need of some advice please!

 

I've been looking round for a replacement C10 when I suddenly realised im not sure what value its supposed to be (I'm certainly no electronics technician!), the schematic says 471/1kV, is that 0.471 microfarads / 1000V? also what kind of capacitor is it? a decoupling ceramic disc capacitor or metallised ceramic plate capacitor or what? They all look the same to me and I dont want to mess this up!!

 

Also my mid pot is damaged from transit, all the schematic says is A250k. No mention of maximum wattage or voltage. Here in Hull noone sells 250k pots. The nearest I can find is 220k 0.2W 500Vdc logarithmic, would that be safe? I dont want to kill my amp or myself!

 

Cheers

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