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Post subject: Re: new Bronco day
Posted: Mon Feb 09, 2015 4:56 pm
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Retroverbial wrote:
Don't forget to RAWK when the upgrades are complete.

8)

Arjay


RAWK ; mean ?


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Post subject: Re: new Bronco day
Posted: Mon Feb 09, 2015 6:02 pm
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stratele52 wrote:
Retroverbial wrote:
Don't forget to RAWK when the upgrades are complete.

8)

Arjay


Oh hell yeah!!!

RAWK ; mean ?



That would be Western slang for Rock. :D

One more quick question, 40/20/20 per Bronco specs or 20/20/20 per vibro champ specs? And what would the difference be, if any?

Thanks

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Post subject: Re: new Bronco day
Posted: Mon Feb 09, 2015 7:28 pm
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socal323 wrote:
stratele52 wrote:
Retroverbial wrote:
Don't forget to RAWK when the upgrades are complete.

8)

Arjay


Oh hell yeah!!!

RAWK ; mean ?



That would be Western slang for Rock. :D

One more quick question, 40/20/20 per Bronco specs or 20/20/20 per vibro champ specs? And what would the difference be, if any?

Thanks


There doesn't seem to be any rhyme or reason to it. All VCs/Broncos (at least through '75) originally had a 20/20/20/20ųf 450VDC Mallory Cap Can.

I've seen some (such as my '65 & '68 VCs) which simply didn't use the fourth 20ųf Cap at all so all 3 circuits are filtered @ 20ųf . But, I've seen others (all unmolested originals), where the 3rd & 4th Caps are wired in Parallel changing the circuit filtering to 40/20/20ųf and using all 4 Caps in the can. The schematics for all the VCs I've seen call for 20/20/20, but for some reason, they weren't all built that way and it's not unusual for the schematics to be inaccurate.

I never traced the circuit back to see if any other components used (resistor values, different Tubes or such) necessitated the increase. Whichever case, I doubt the difference is even noticeable.

Maybe someone can enlighten?

cheers!

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Post subject: Re: new Bronco day
Posted: Mon Feb 09, 2015 9:16 pm
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" 20/20/20 per vibro champ specs. " This is the one to use. Get the one rated at 525VDC.

Be sure to change the bypass cap coming off the 6V6GT cathode-to-ground. Use a 25mfd/50VDC cap. Measure the 470-ohm, 1-watt resistor. If off by more than 5% --- go to a 470-ohm, 2 watt, 5% tolerance metal oxide.

Good luck! Great amp.


http://bmamps.com/Schematics/fender/bronco_aa764.pdf


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Post subject: Re: new Bronco day
Posted: Fri Feb 13, 2015 8:12 pm
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Received the CE cap can today and took on the challenge of replacing the old one. Here are the pics of 2 hr. ordeal. Helps to have the right tip for your soldering iron when removing the old one.....i didn't :cry: :cry: .

Here's the removal of the old one.
Image
Here's the install of the new one.
Image
And the final product.
Image

Now I know what all the fuss is about having to replace the cap can, major hemerrhoid. But nothing beats the satisfaction of doing it the right way.

Thanks to all for all your advise and suggestions. I'm just waiting on the speaker now, but with the new multi section cap can I've already heard an improvement. With the new speaker this baby is gonna scream. :D :D

Can I get a whoop whoop? :lol: :lol:

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Post subject: Re: new Bronco day
Posted: Fri Feb 13, 2015 8:27 pm
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Abe,

Very good job. With those Ohmite resistors and CE can --- amp should be good to go, for the next 25 years.


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Post subject: Re: new Bronco day
Posted: Fri Feb 13, 2015 8:41 pm
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Schweet!

8)

Arjay

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Post subject: Re: new Bronco day
Posted: Sat Mar 07, 2015 12:20 am
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Just got back from a business trip to find this waiting for me, wooo hoo!!

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I know what I'll be doing tomorrow. :D :D

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Post subject: Re: new Bronco day
Posted: Sat Mar 07, 2015 12:24 am
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That should provide a significant improvement.

Arjay

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Post subject: Re: new Bronco day
Posted: Sat Mar 07, 2015 6:53 pm
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Well it's all complete, new cap can and new speaker installed and the amp sounds amazing. It's got a very pronounced clear and chimey sound and the vibrato is to die for. The low end is nice and tight and it has a very smooth breakup. :wink: This is now most definitely the best living room/practice amp I've had the pleasure to own.

The only other thing I did was replace the 25uf 25v cathode cap with a 22uf 50v. When making my measurements I was getting a reading of over 25v through that cap. No Bueno.......

I also experimented a little bit by changing the cathode resistors value to bring the power tubes output down to around 14 watts. I was not happy with the results, the bass got flabby, it broke up earlier but in an unpleasant way, and the vibrato intensity got weaker. I had heard about some folks replacing the 470 with a 1k with good results.......well this amp didn't take to kindly to that so 1k out and 470 back in. I know it's running on the hot side but there doesn't seem to be any heat damage on the chasis and the tube isn't red plating so the 470 ohm resistor is here to stay. If it eats up the tubes a bit faster, so be it. As Jim Campilongo put it, sometimes you have to sacrifice tubes for tone. :D :D

Anyways, I just thought I'd share those results and as always, ymmv.

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Post subject: Re: new Bronco day
Posted: Mon Mar 09, 2015 6:46 am
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Abe, the 6V6GT is running in a hot Class AB1, pseudo Class "A." When you drop the idle bias current in most single-ended output stages too much --- the tone suffers very badly. I can't remember exactly why, but it has something to do with the output tranny-output tube interaction.

BTW... another way to set the idle bias is to change the grid-to-ground resistor. Most Champs and VC's have 220k-ohm resistor. Decreasing the resistance (to say 140k-ohms) lowers the idle bias. SE amps are sensitive to this change, also. I've heard of ppl playing with both cathode tied and G2G resistor values to get the "right" tone. Some even use a rheostat on the cathode and dial-in the resistance. While changing the set resistor on the grid. I've never done this --- as the 470-ohm/220k-ohm combo seems to be the best.

Use a good 6V6GT and the tube will last nearly as long as a 6V6GT in push-pull setup.


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Post subject: Re: new Bronco day
Posted: Tue Mar 10, 2015 6:51 pm
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Yeah, I don't think I'll be doing anything else to it for a while. I'm pretty happy with it now.
The current 6v6 is a raytheon 6v6gta. If I do end up replacing it in the future I think I'm gonna opt for a brighter toned 6v6gt. That weber speaker is REALLY pronounced on the low end. Tight and puchy but need to keep the bass knob waaaaaay low. I think I'm gonna try a tung sol 12ax7 first, see if that brightens it up a bit more.

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Post subject: Re: new Bronco day
Posted: Tue Mar 10, 2015 8:17 pm
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Abe, may want to try a 5751 or even 12AY7 in the 12AX7 input position. A good 5751 to try is the GE JAN-JG 5751.


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Post subject: Re: new Bronco day
Posted: Sun Apr 30, 2017 8:00 am
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Time for an update.

As much as enjoyed the Weber for its increased volume and low end contribution, I ended up sticking the original alnico oxford back in. All I can say is that this is "the" speaker that should be in this amp.
I love the breakup of the the speaker at higher volumes and the extra high end sparkle. It's very reminiscent of a 5f2a princeton circuit.
At least for me, the search is over....even though I'm right back where I started. :D
This speaker with this amp is the epitome of a simbiotic relationship.
Just thought I'd share.

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Post subject: Re: new Bronco day
Posted: Sun Apr 30, 2017 9:18 am
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How much break-in time did you allow the Weber?

Arjay

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