Відео

I repair electronic musical instrument gear and as part of this I modify tube amps. This series of videos was posted to highlight the amp after mods for potential customers.

its a push pull gain boost

The speaker is the V30 that came in the amp. The mods are fairly drastic changes to the circuit on both channels.

I have the combo version of this amp and the reverb is quite huge sounding. The cable going to the reverb tank is extremely short and can pull off easily which happened to mine during shipping. The pin actually broke so I had to replace it and I used a longer cable as well to prevent further issues. It’s a pretty easy check to do and you won’t need to break into the upper chassis.

Nope. Guitar to head to 212 cabinet.

This was a customer owned unit.

I took my logo off this head as well In 91 and I still use it with out that logo on a vintage Marshall 412 cab -- the logo was just to metal pointy vibe for me - looks nicer with out it and grabbed me when I saw this video … just like mine

I am most active on Instagram...which is not very active. Too busy fixin and modding cool music gear. Please Email info@madcowamplification.com with any questions.

The clarity of the drive channel is greatly improved with the mods as well as a more balanced EQ. The gain is much less “fizzy” after the mods as compared to a stock Classic 50. More organic, dynamic and responsive while being less harsh and compressed.

@@racmusiccom What would something like that cost? Do you do that kind of thing? I've never shipped anything that big. Sorry

@@Rainman66 yep, these are mods I developed for a customer several years ago and have repeated many times. Please email info@madcowamplification.com and I’ll reply with pricing, details how to ship, etc.

I live and work in Ohio, USA. Please email for pricing and details - info@madcowamplification.com

Agreed. Which is why I adjusted the bias on this unit by adding a 33k parallel to the stock 22k resistor to make the negative fixed bias voltage more positive. Which increased it to 60% idle plate dissipation. While most tubes produced 60 years ago could handle biasing for increased idle plate dissipation in excess of 70%, I’ve found current production tubes become less reliable at these increased operation. In addition I personally have found most players don’t notice a significant tone / response difference to justify the increased idle plate current. In fact more have found they prefer the more moderate 60% IPD which allows for greater swing positive and negative without reaching saturation or clipping.

@@racmusiccom it seems like you're castrating the amp.

@@MAP448 only if you lack knowledge and experience in tube amp operation ;)

www.thetubestore.com/lib/thetubestore/schematics/Peavey/Peavey-Classic50-Schematic.pdf You may be confusing each half of the 12AX7 dual triode as being an individual single triode tube. In which case, you should not be inside the amp in the first place.

@@racmusiccom pfff. Let the guy discharge his caps and figure it out. You techs act like nobody has business learning how to work on their amps. It's not like people can just easily go to tech school or find a mentor.

Sorry for the slow reply. I obviously don’t check UA-cam account often. There is a chance you have a damaged resistor in the filament supply that is causing the hum. You should really have a qualified tech check it out. And these amps routinely average 90-110% max plate dissipation at idle. IE wayyyyy to hot. The short of it is that every Blues Jr really needs to have the negative bias voltage increased so the tubes will run cooler and not flame out like they often do.

Just move the decimal point one place ;)

Quite frankly if you need that information via UA-cam you shouldn't be doing it in the first place

Thanks for the kind words!

Phillip Holmes yep, factory circuit in the Blues Jr is fixed negative bias. And my preference is to mod the bias circuit and add a 10k bias pot to the chassis so it is easily adjustable in the future. But adding a resistor parallel to R51 or R52, depending if more or less negative bias voltage is needed, will get it done without having to pull the main pcb.

ijams sum no EL84 is made to withstand dissipation exceeding 100% at idle. Bias adjustment is a necessity if you want a Blues Jr to operate reliably.

@@racmusiccom I have a hot rod blues jr iv with a black pc board. It seems to be built much better than the previous versions. I have had it a little over a year now & I play it average 2-3 hours a day, everyday since I ordered it from fender. Never changed anything on it yet & it plays & sounds better each & everyday. When I decide to replace the power tubes, I will order the same tubes from fender & I shouldn't have to adjust the bias. So many people trying to reinvent the wheel.

@@MAP448 the output section of most recent revision Blues Jr (IE black pcb) is drastically different than earlier v4 green pcb revision. The most recent black pcb revision has a cathode biased output section. Generally this type of circuit is very forgiving as far as the bias point varying little regardless of the operating rating of the tube. Where as a fixed negative voltage biased output section (all Blues Jr revisions leading up to the current black pcb) is not as forgiving. So in fact the engineers have “reinvented the wheel” with your Blues Jr ;)

@@racmusiccom a lot of fender's amps in the past were cathode biased. They didn't reinvent it with the bj4

@@MAP448 the handful of early tweeds, a few brown tolex models, the black champ and bronco…and I’m sure a few more after that escape me at the moment. Let’s say “several” other Fender amp designs have utilized a cathode bias output section as to not be mis-lead and mis-inform others. My point was that you said “reinvent the wheel” as if to imply that adjusting fixed negative bias voltage for an idle plate dissipation around 60% would negatively impact the performance of the amp. More times than not, adjusting the bias will actually improve performance of most units with the non-adjustable fixed negative voltage bias circuit as with the one shown in this video. In fact most units typically operate in excess of 100% idle plate dissipation and eventually fail catastrophically causing excessive damage to the amp if such adjustment to the bias voltage is not done.

strat cat71 without adjusting the bias on the Blues Jr you’re rolling the dice on catastrophic failure.

The bias circuit is identical on all Blues Junior revisions.

Not really a mod but increased value of cap across the plates of the phase inverter and jumper added to solved ground issue with output jacks. Google for more info.

Thanks for the kind words!

Sovtek have their uses. I generally use JJECC83S in most high gain circuits unless the customer is looking for a particular response that a different tube is better suited for.

Thanks for the kind words!

Thanks for the kind words.

You might need a tube screamer in front of it to do "modern tones/metal tones"

Get it you wont regret it.

Luke Walker yes. It can do modern tones as well.