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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 6:50 am
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BMW2002Ti wrote:
One suggestion... physically move the cathode-tied resistor (off the 6V6GT tubes) AWAY from the bypass cap. That resistor gets hot and can heat that cap. Heat can change the cap's electrical behavior and thus change the idle bias of your 6V6GTs. Here's how I did it, in one of my Reverb Unit (which is driven by 6K6GT cathode-bias amp.

Image


+1

Thermal exposure can definitely be a factor in value consistency (and overall component life).

Arjay

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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 2:04 pm
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With amp off... measure the resistance between grounding point(s) in question and the chassis. If static DC resistance is above a couple ohms --- look to improve grounding. If not, don't worry. You want to avoid ground loops.

Done all ground resistance is about the same .5 ohm.

The cathode resistor sits off the board about 3/8" and is about another 1/4" from the 25uf cap. Its hard to see from the photo I posted due to the angle.

I took the p12r out and set it aside for now. I put the c12k back in the DRRI and put the Weber 12a150 in the TV.

New issue, hooked the Weber up as the p12r was with respect to wire orientation. Speaker sounded like crap low output shut it down, noticed the rectifier was over heating...
However the Webers speaker terminals are marked red on one side the other is unmarked.
Is it the black or the green that goes to the red terminal from the OT?


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 2:21 pm
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Black was traditionally used to designate ground but I think you've got other issues at play. With a single speaker, phasing is not a factor.

Arjay

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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 2:34 pm
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Thanks Arjay, didn't think the phase caused the overheat, as I had the blk on the red. But I do think the 5y3 is toast.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 3:43 pm
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Possible, but before you hazard another rectifier tube you might want to determine what happened the first 5Y3 and (more significantly) why.

Arjay

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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 3:57 pm
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Yeah, trying to figure that out. I put the old 5y3 that came with the amp back in. Worked fine?
OK, looked at all the vac spots incoming was fine 119ac at the fuse and the on/off switch.
5y3, Pin 8 was 4.9ac but pin 2 was 6.2ac. I expected 5 at each, are they close enough or is the 6.2 to high?
The dc at the plates was about the same as w/ the tube that overheated.
V1 85vdc
V2 160vdc
V3 363vdc
V4 363vdc

guitar played and speaker sounded fine.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 4:13 pm
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Yeah, sounds like the 5Y3GT had a short. Was it the WGT?

I have some if you wish, to have backups.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 4:24 pm
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Thanks, no problem I have 1 more 5y3wgta. Just using the one that came in the amp for now though until I figure it out.

Also, the reading to ground I'm getting .45vdc is closer to what the layout from the tube amp book stated. I missed the decimal point and thought it was 9 vdc from the schemo/layout you posted. And to boot it is the same resistance I get to ground from anywhere on the chassis. So it may be just that difference, the various resistor drifts from stated #'s. I had to blow up the view to 200% to notice the decimal place. So overall, the numbers are all pretty close and tubes fail. I think I'm good and better off w/ the Weber as far as the low freq. farts, still it is only the 25watt version but is more stable than the old p12r.

appreciate the feedback


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 6:28 pm
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sfceric64 wrote:
...but is more stable than the old p12r.


Is that P12R an imported re-issue or a Chicago-made original?

Arjay

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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 8:41 pm
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sfceric64 wrote:
And to boot it is the same resistance I get to ground from anywhere on the chassis. So it may be just that difference, the various resistor drifts from stated #'s. I had to blow up the view to 200% to notice the decimal place.

So overall, the numbers are all pretty close and tubes fail. I think I'm good and better off w/ the Weber as far as the low freq. farts, still it is only the 25watt version but is more stable than the old p12r.

appreciate the feedback



Well... grounding seems ok. Farting is an issue. What mfd bypass caps are you running on those input/gain stage tubes? Try removing one leg of input stage triode half bypass cap. Listen to amp. See if that helps the farting.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 8:52 pm
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Is that P12R an imported re-issue or a Chicago-made original?
Straight outta Chicago, Arjay. Although it may have been reconed I believe its a 1949 p12r coded 220932 p12rc48972. It weighs 3lbs 1oz and has a smooth cone w/ a 1" voice coil. It has the gold pm speaker concert series label, but it is in poor shape-wrinkled.

Quote:
Well... grounding seems ok. Farting is an issue. What mfd bypass caps are you running on those input/gain stage tubes? Try removing one leg of input stage triode half bypass cap. Listen to amp. See if that helps the farting.
It performed superbly after supper tonight for about 1 1/2- 2 hours, I couldn't be happier with it.. :mrgreen: It is nearly as loud as my DRRI and the Weber sounds exactly as it should.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 9:26 pm
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So, no more farting.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 9:42 pm
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Quote:
So, no more farting.
None, but I'm getting bad GAS for an ABY pedal. :lol: :lol:


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Aug 29, 2016 10:04 pm
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sfceric64 wrote:
Straight outta Chicago, Arjay. Although it may have been reconed I believe its a 1949 p12r coded 220932 p12rc48972. It weighs 3lbs 1oz and has a smooth cone w/ a 1" voice coil. It has the gold pm speaker concert series label, but it is in poor shape-wrinkled.


The "48972" code is a customer number and with its smooth cone, I'm guessing that the speaker was a pull from a console organ (these frequently used a pair of speakers that included one ribbed and one smooth cone). If the coil/cone is original it's rated for 20 watts -- usually 25 if re-coned with modern-spec components. And if the basket is teal-colored the speaker likely was made in 1959. AFAIK all of the Jensen speakers used in Fender amps (regardless of era) had the ribbed cone.

Arjay

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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Tue Aug 30, 2016 10:29 am
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I don't doubt you a bit but I'm leaning towards it being about 15watts(Dave Hunter's The guitar amp handbook)The re-cone looks to be a DIY job that's not to tidy. I feel it would work sufficiently in a Champ or maybe an early Princeton. The weight is what I can't pin down, the original p12r weighed in at 3lbs 5ozs. Mine is 4oz light and in Alnico speak you know that means less wattage/power. I'm assuming the magnet was switched as there is evidence of adhesive slop around the join of the magnet, the rest of the cone(albeit smooth) and voice coil dust cover looks fairly tidy as well as the basket. Maybe my assumptions are wrong and it is a 1959 organ speaker w/ a gold(pre late 57/58) label. That could be the case or the bell cover is from another speaker entirely. What "customer" does the code indicate? Definitely not a Rhodes-Fender, they used a single 3.5ohm speaker early on. To hard to say from what I can resource. But it is the only disappointing point of the amp from my perspective. As a side to the color "teal" (here in Texas teal is a bird of the duck variant commonly blue and green and quite tasty grilled and stuffed) it is the exact basket type but (OD) green color of the speaker pictured on page 4 of this thread.


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