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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Tue Jun 02, 2015 6:02 pm
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Congrats, on the fix! :D :mrgreen: :D

Metal oxide is fine in the PI section. These will tend to give you a brighter tone. They will be stable for a long time.

Yeah, playing with the tone stack will help tailor the amp more for guitar use. D/L the Duncan Tone Stack Calculator, if you already haven't. It'll help you with specific component values.


http://www.duncanamps.com/tsc/download.html


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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Tue Jun 02, 2015 8:50 pm
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If you look into it, you'll find that there is no merit to using CC resistors anywhere in an amp, there is no magical tone from CC resistors, it's simply a myth. This myth probably stems from the simple fact that this is what was used in vintage amps. Why? Because this is all that they had, except more expensive WW, which would be overkill.

I have swapped CC and FP resistors in a couple of amps, back and forth, and there is simply no difference in tone. I am referring specifically to Plate resistors, which would be the only possible place for any tone difference,......that is if the voltage swings were actually high enough to take advantage of the slight inductive difference in resistors, and those voltage swings are not near high enough for that.

Fact is, FP are more stable, have better precision, and they don't catch fire if they fail. FP = Flame Proof, which is another reason NOT to use CC. :wink:

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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Wed Jun 03, 2015 3:38 am
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The only sad thing is, we will never know which change fixed the issue :roll:
except that the unmolested "normal" channel was positively affected and so I have to lean towards the modding of the Phase Inverter circuit as the culprit.
in fact now I prefer the normal channel with the deep switch on, go figure, sounds more like my 68

The new electronics store I found in a neighboring town has a wall of Metal oxide / Flame Proof with a HUGE selection of values in 1 watt and 2 watt, I go in there and spend ten bucks and have a huge supply of my own.
compared to ordering online and waiting 7 to 10 days , It is rather nice :D
Wish they stocked mallory 150's my favorite coupling caps.

Those 6L6WXT+ tubes are still running 32ma with the bias cranked, the other pairs of 6L6GC's ran at similar ma but at about half on the bias pot, so Its not the amp, its the tubes, sadly my other used 6L6's don't match close enough.

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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Wed Jun 03, 2015 7:03 am
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blues bondsman wrote:
The only sad thing is, we will never know which change fixed the issue :roll:
except that the unmolested "normal" channel was positively affected and so I have to lean towards the modding of the Phase Inverter circuit as the culprit. In fact now I prefer the normal channel with the deep switch on, go figure, sounds more like my 68.

The new electronics store I found in a neighboring town has a wall of Metal oxide / Flame Proof with a HUGE selection of values in 1 watt and 2 watt, I go in there and spend ten bucks and have a huge supply of my own.
compared to ordering online and waiting 7 to 10 days , It is rather nice :D
Wish they stocked mallory 150's my favorite coupling caps.

Those 6L6WXT+ tubes are still running 32ma with the bias cranked, the other pairs of 6L6GC's ran at similar ma but at about half on the bias pot, so Its not the amp, its the tubes, sadly my other used 6L6's don't match close enough.


Oddly enough, the 1968 Bassman I have, also had a bad tail-resistor network on the phase inverter. The one-meg (330k-ohm on your Bassman 10) grid-to-ground resistors were way off. Like 2-3 meg ohms, each. I also used metal oxide or FP resistors.

Image


Nice to have a parts shop nearby. Those days are over, where I live. No more Marvac... :(

The new Tungsol (Russian) 7581 are about the strongest tubes out, at the moment. Nice powerful tone. But, not the rich midrange potential of an NOS RCA or GE.

http://www.tungsol.com/tungsol/specs/7581-tung-sol.pdf


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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Thu Jun 04, 2015 3:58 am
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Speaking of coupling caps, wow ! beemer those .1's are HUGE ! and look like torpedos LOL

One nice thing is that I was sure i would hear the "repaired" cones on two of the speakers after the circuit was stabilized and yet the sound is tight and the low end solid as a rock now, no buzzes, no fizz 8)

changing the .047 for a .027 (the orange drop you now see) and putting in a 220pf in place of the 500pf in the Studio channel changed the character of this amp completely, I put a 5751 in V-2 too see how it would sound
The overall impression is now so very close to a typical 50 watt bassman head, the 4X10 speakers obviously have an effect on the punchiness and attack of the amp.

My opinion:
don't pass up a 75 or newer Bassman 10, it may take some work and a little modding, but its worth it !
The only regret is that you really only have one choice for speakers in 32 ohms, running 8ohms in series / parallel will get you to 8 ohms too I guess so..........................
Now a new baffle cut for 2x12 opens up a lot of possibilities as most good 12"s are available at 16 ohms
But since you already have a cab built like Herman Munster :lol: you might as well keep the goofy 4X10 32 ohm set up, its unique character is what sets it apart right !

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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Thu Jun 04, 2015 7:40 am
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Chris, glad it worked out. Those caps are Russian mil spec, paper-in-oil K40Y-9 metal-clad caps. 1000VDC rated. One day try the 630 or 1000VDC rated ones in amps. And 200 or 400VDC for guitars. Very nice, for the price.


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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Wed Jun 10, 2015 12:47 pm
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Here ya go guys
I put together a few minutes of sound clip of this amp
The Tascam DR-05 takes a bit to auto level so hang in there
Normal channel, then Normal with deep switch and then Studio channel, all straight guitar (no effects)
My 50th stratocaster neck pickup only

https://app.box.com/s/aovitg3kuzkyovd00g80la57v9re0jbf

Just some blues noodling to show you how she sounds, boosting and some compressor (the way I like it) and its even better !!!

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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Wed Jun 10, 2015 5:05 pm
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Very nice, clean tone.

Thanks, for posted the sound clip.


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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Thu Jun 11, 2015 6:03 am
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It is still pretty dark and woofy with three of the original (made for bass) speakers in there
I'll exchange one more for another Jensen Mod 50 and I'll bet it opens up some more.

Bummer that eminence does not make a copperhead or Ragin Cagin in 32 ohm, probably wouldn't sell a bunch
Cutting out the baffle area and installing cleats to hang a new 2X12 might be fun, Lots of 16ohm 12" out there to choose from.

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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Thu Jun 11, 2015 8:56 am
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blues bondsman wrote:
...running 8ohms in series / parallel will get you to 8 ohms too I guess so...


Why not this?

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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Thu Jun 11, 2015 9:54 am
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Why not ?
then I would have to replace all and I already invested in one 32 ohm
so.............................
Sounds great now, my guess is one more 32 ohm Mod 50 and it will balance out well
It will have two smooth cone low wattage and two ribbed cone 50 watt speakers, should be very dynamic

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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Mon Jun 22, 2015 10:27 am
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So I just got a Bassman 10 in for service. It looks a little different than this one though.
It has vents on the side and an accessory AC recptacle and a hum balance pot on the back
The PT and OT date code is 606-842
The amp is rated at 70 watts with 2 X 4Ohm outputs and puts out a healthy 67 watts at 4 ohms with the new JJ tubes.
So I got the whole amp straightened out with the exception of the speakers. One was hooked up backwards and is now open. Poor thing musta spent its whole life bucking his brothers.
Anyhow, the other speakers measure 13 ohms and I need a replacement. I'm inclined to go 8ohm with a 4ohm resistor unless anyone has a better idea The customer is unlikely to go for a new set.
The speaker codes are 014213 and 109 8832. 10" ceramics
.


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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Mon Jun 22, 2015 11:09 am
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The "1098" EIA code indicates a Pyle speaker. They have no redeeming social or sonic value. Replace it with any quality 16-ohm speaker (a bass driver if your client specifies it). The amp itself seems to date to mid 1978, likely one of the last Bassman 10's produced.

Arjay

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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Mon Jun 22, 2015 8:30 pm
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Thanks, Why Google when I can Arjay...


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Post subject: Re: 1970's Bassman 10 project just came in
Posted: Mon Jun 22, 2015 10:18 pm
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TimsAudio wrote:
...the other speakers measure 13 ohms and I need a replacement. I'm inclined to go 8ohm with a 4ohm resistor ...


DC resistance does not equal impedance. If you measured 13 ohms DC resistance, the speaker is probably rated 16 ohms impedance. :idea:

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