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FDP Forum / Fender Amps: Vintage (before 1985) / 6G6-B owners: Do ur bass controls respond & what up w/norm. chan. treb.?

Next 20 Messages  
seven-7

U.S.A.

When in doubt, crank it!
Feb 20th, 2006 12:16 AM   Edit   Profile   Print Topic   Search Topic

Hi,

Helping my father with his '64 6G6-B. Amp is running NOS mid-80s Philips 7581As with similar era Philips 12AX7WAs. 7581As biased 445V @ 31mA (he likes it clean). Did a filter cap replacement, but later he said the normal channel lacked power. Says he has to "turn it up a lot" on the normal channel to get it loud (which he compares to my Bassman, an AA864, which gets loud earlier.). Checked all plate and grid voltages from output to normal channel, everything checked out fine. No DC leakage on the grids of the normal channel. While I was in the amp, we decided to replace the original Astron 25uF+25uF cathode bypass caps and the bias cap.

I don't think the lack of gain in the normal channel is really all that drastic (I guess the normal channel has less gain due to only one tube compared to two in the bass channel?), but what I find odd was that the bass control did not make any difference to the tone whatsoever on both channels. I find it odd that both channels' bass pots could be bad...

Also, I noticed that the treble control, when turned all the way down on the normal channel, completely cut the sound (with the volume mid-way up). As you increase the treble, the signal gets louder more than it gets brighter. Between 4 and 5 on the treble, the signal gets significantly louder and only past 5 does the tone get brighter.

My question: are these artifacts "normal" with the brownface Bassman circuits or is there something else I am overlooking in the amp? Sorry, the only point of reference that I know is a AA864 Bassman which doesn't have these "features"/"problems".

Any help from the gurus would be appreciated. Thanks for your time.

milocj
Contributing Member
*

Dearborn, MI

Feb 20th, 2006 04:20 AM   Edit   Profile   Print Topic   Search Topic

I don't know the technicalities of how or why that works, but it seems to be pretty consistent with my 1964 6G6B. The Normal channel is about one number or so quieter on the volume control than the Bass channel, and neither channel seems to start getting what I would consider loud until 4 or 5.

The treble controls don't seem to do very much until 5 or higher and at that point they seem to make a sudden jump in how much treble is in the mix as well as make the amp louder. The bass controls don't seem to have much effect until they get around 6. They still don't add that boomy bottom end like my blackface amps but there is a definite difference in the sound.

All of the controls seem to be much more interactive on this amp than my BF Fenders so there was a lot of experimenting to find out how to set one to get the others to work a certain way.

Tom Loizeaux

Baltimore, MD, USA

Feb 20th, 2006 07:33 PM   Edit   Profile   Print Topic   Search Topic

No, this is not normal. It sounds as if your bass control, or related componants, are not working.
The blonde Bassman should perform in a manner very similar to the '64 Bassman.

Tom

seven-7

U.S.A.

When in doubt, crank it!
Feb 20th, 2006 08:12 PM   Edit   Profile   Print Topic   Search Topic

Any idea of what I should look for that I haven't already done?

Thanks!

RussB
Contributing Member
**

Connecticut

a little out of tune
Feb 20th, 2006 08:21 PM   Edit   Profile   Print Topic   Search Topic

Some late 6G6-B's have a circuit variation that ISN'T documented in any schematic...IIRC, it revolves around the bass pot wiring.

The BASS channel is a bit "quieter" than the normal channel, it's just the nature of the (Blonde) beast.

I've added a close-up pic of the BASS pot of a '64 transition 6G6-B. This is how the bass pot was wired from the factory, and as you can see, it varies from the 6G6-B schematic.

The owner of the amp complained of a lack of bass response from the bass channel. reverting it back to the "correct" layout gave the amp a big bass boost.

I felt a bit guilty changing it over, as this was how the amp came from the factory. But in this case, good tone was more important.

bass channel bass pot

seven-7

U.S.A.

When in doubt, crank it!
Feb 20th, 2006 10:11 PM   Edit   Profile   Print Topic   Search Topic

Russ,

Great info! I'm thinking that this has *got* to be the same situation with my father's amp! Over the next weekend, I will take a look and double check the wiring. I don't know if he'll go for the change if it indeed is wired "incorrectly" - he moaned and groaned when I suggested to change the nearly 42 year old original Mallory bias cap and Astron cathode bypass caps (although he had no qualms about me changing the original filter caps)!

milocj
Contributing Member
*

Dearborn, MI

Feb 21st, 2006 02:00 PM   Edit   Profile   Print Topic   Search Topic

If it is indeed wired incorrectly you've got to convince him to change it. The controls on mine don't respond in the same way that the controls on my BF amps do (although I don't have a BF Bassman for comparison) but they do work and result in changes to the tone.

I didn't realized that you said "no change in tone whatsoever".

seven-7

U.S.A.

When in doubt, crank it!
Feb 21st, 2006 02:29 PM   Edit   Profile   Print Topic   Search Topic

Yes.

With RussB's explanation, I'm thinking this happened on the transitional 6G6-Bs (i.e., mid '64 with black Tolex and white knobs) which is what my pappy has.

I gotta wait until the weekend to confirm.

seven-7

U.S.A.

When in doubt, crank it!
Feb 27th, 2006 03:09 AM   Edit   Profile   Print Topic   Search Topic

Russ,

You da man! Thanks!

When I compared to the 6G6-B schem, the normal channel's bass pot had the brown wire tied to the middle terminal (along with the yellow wire from the 70k tap from the treble pot) instead of directly to the 70k tap. And the bass channel's bass pot (5k incidently, not 25k according to the schem) was weird, it had a 4700 ohm resistor on the terminal connecting it to ground that normally (according to the schem) is not connected. The other terminal that normally (again according to the schem) has a 820 ohm resistor connecting it to ground was simply bent and grounded to the back of the pot. Also the yellow wire going from same terminal to the 0.25uF cap was missing.

Needless to say, after rewiring the amp the controls are working great.

One thing, though. I noticed that the tube chart inside the amp shows 6L6GC and not 5881s which is what I thought all 6G6-Bs specify. Does that mean I can't use the Tung-Sol 5881s we have in there now (440V @ 37mA)? Moreover, is it bad to run the plates at 440V (rated max = 400V) despite the fact that the calculated dissipation seems safe at ~70% (16W) of max. (23W)?

milocj
Contributing Member
*

Dearborn, MI

Feb 27th, 2006 06:47 AM   Edit   Profile   Print Topic   Search Topic

My tube chart shows 6L6GCs, too, but I've been running some old RCA 5881s in it with no problems and I love them. I was told that they probably wouldn't hold up as long as a 6L6GC.

There have been some posts about why some of the older Bassman amps called out for 5881s when the voltages seem too high and 6L6GCs were already in production but I don't think I've ever seen an explanation.

milocj
Contributing Member
*

Dearborn, MI

Feb 27th, 2006 01:52 PM   Edit   Profile   Print Topic   Search Topic

Well,
You guys made me go and dig up the pictures I took of mine when I did the recap on it. My normal channel matches up to the schematic but it looks like my bass channel is wired the same way as seven-7 is describing. The second .25uF cap from the right is going straight to ground and there is no wire going from it to the pot.

Being as mine and seven-7s were wired the same way do you think this was a running circuit change? My bass channel is voiced much differently than the normal channel but I figured it was supposed to be this way. All of my controls work, they're just more interactive than on my blackface amps.

My 1964 6G6B

(This message was last edited by milocj at 02:30 PM, Feb 27th, 2006)

RussB
Contributing Member
**

Connecticut

a little out of tune
Feb 27th, 2006 04:28 PM   Edit   Profile   Print Topic   Search Topic

Yep, this appears to have been a circuit change that never got a new designation (6G6-C?) Leo must've been too busy getting the "Blackface" line ready...

There's that friggin', 70% thing again! That is the MAX you should run the tubes at, NOT a target! You are running them nice old 5881's hard!

seven-7

U.S.A.

When in doubt, crank it!
Feb 27th, 2006 04:35 PM   Edit   Profile   Print Topic   Search Topic

Hi miloj,

That actually looks like the normal channel, and yes that's how my dad's pot looked as (mis)wired from the factory. If you look at the layout, the brown wire should go to the 70k tap of the treble pot, but it instead goes to the middle terminal of the bass pot.

You never know, maybe the guy/gal wiring 6G6-B transitional Bassmans in August '64 was new?

Do you have a pic of the bass channel?

seven-7

U.S.A.

When in doubt, crank it!
Feb 27th, 2006 04:44 PM   Edit   Profile   Print Topic   Search Topic

Russ,

I can't see that this variation was intentional. I mean, the pots didn't work! How did these amps even pass QC? My take on it is someone new must have just started wiring 6G6-Bs in the summer of '64! =)

Also, the 70% thing... maybe I didn't make it clear, but that is the setting my father liked the best, we didn't target for it. I now realize that 440 @ 38 = 73.8% What disadvantages/dangers (besides shorter tube life expectancy) can we expect running the Tung Sols like this?

Thanks!

(This message was last edited by seven-7 at 04:53 PM, Feb 27th, 2006)

milocj
Contributing Member
*

Dearborn, MI

Feb 27th, 2006 05:16 PM   Edit   Profile   Print Topic   Search Topic

You must not have slid the entire picture over because the bass channel is real clear on the right hand side. I did notice after posting that picture that my normal channel appears to be the same as yours, too. I thought it was correct at first because I could make out that the wire was soldered to the tap on the treble pot but then I realized that it changed color and must have been done backward. My normal bass pot worked fine, but the response was all above 4 or 5 and the higher the treble was up the better this pot worked.

At first I was thinking that this could have been an accident, but on the bass channel they actually grounded that one .25uF cap to the chassis and didn't even place that wire into the circuit. It sure looks deliberate to me especially with all three of our BFWK versions being wired that way. I don't know enough about circuits to know what they hoped to accomplish by making this change, though.

Now I'm going to have to try it on my amp even though I'm really happy with the way it sounds already. I guess I can always put it back. Did you cut the ground wire that soldered to the brass plate behind the faceplate?


RussB
Contributing Member
**

Connecticut

a little out of tune
Feb 27th, 2006 05:45 PM   Edit   Profile   Print Topic   Search Topic

I've seen 4 late 6G6-B's wired like that...could be a factory blunder, who knows?

shorter tube life would be the only negatives...if it sound good, go for it!

seven-7

U.S.A.

When in doubt, crank it!
Feb 27th, 2006 07:18 PM   Edit   Profile   Print Topic   Search Topic

milocj,

Sorry, you're right, I didn't look at the right side of the pic. But that's *it*! Looked exactly like my dad's.

About the 0.25 cap, I actually just wired it to the terminal on the bass pot [that has the 820 ohm resistor connected to it in the schematic], I didn't actually look to see if it was grounded to the brass plate. I guess now I need to ask him to open up the head again... he won't be pleased. =( I guess leaving that 0.25 cap connected to ground doesn't make sense if I have it also connected to the same terminal on the bass pot that has the resistor on it (according to schem), eh?

Russ,

Could there be the possibility that the PT could die sooner because I'm having the Tung Sols draw more current?

Thanks all, especially Russ! That was wild!

jjj333

USA

Feb 28th, 2006 03:22 AM   Edit   Profile   Print Topic   Search Topic

FWIW, here is a link to photos of my bass channel pots and my normal channel pots on my late '63 6G6-B Bassman. The bass channel bass pot is wired according to the layout (unlike the ones being discussed in this thread), but the normal channel's bass pot is wired like the others discussed.

Does it really make a difference if, on the normal channel, the brown wire goes to the bass pot and then has a jumper to the treble pot's tap as opposed to the layout in which the brown wire first goes to the treble pots tap and then has a jumper to the bass pot? I am no tech by any means, so this may be a dumb question.

Also, above, RussB said that the Bass channel is queiter and that is the nature of the blonde beast, however, if I am not mistaken, both milocj and seven 7 said that the bass channel is louder (due to the extra stage of gain). This is how my amp is as well (louder on the bass channel).

Thanks.

My Bassman's pots

(This message was last edited by jjj333 at 03:28 AM, Feb 28th, 2006)

milocj
Contributing Member
*

Dearborn, MI

Feb 28th, 2006 09:37 AM   Edit   Profile   Print Topic   Search Topic

jjj333,
Thanks for the pictures. I was wondering the same thing about the way that the pot was wired on the normal channel and I'm also not knowledgeable enough from the technical end to know if it makes a difference. It sounds like it made a difference on seven's amp.

Did you open up you '63 just to take a look or did you already have those photos? Is the blue capacitor that attaches to the left lug of your bass channel's bass pot also grounded to the chassis near the pots? It doesn't make sense that it would be since it goes to ground through the pot and resistor on your amp.

jjj333

USA

Feb 28th, 2006 02:35 PM   Edit   Profile   Print Topic   Search Topic

milocj--no problem on the photos, I am happy to help out. I had the pictures from when I first got my 6G6-B, so it was no big deal.

Anyways, I looked at the photos for an answer to the question you posed, and you are right, the blue molded cap that is attached to the left lug of the bass channel's bass pot is NOT grounded to the chassis, just the pot.

For seven-7 and milocj, I did a test in which I turned up the normal channel to about 4 and then adjusted the treble pot all the way down and it did NOT cut the volume completely as it did in seven-7's amp. It just significantly cut the treble, then as I turned it up, the treble increased. So this seems to be working normally even though the brown wire goes to the bass pot first and then is jumped with a yellow wire to the tap on the treble pot.

I started another thread in this vintage amp forum, so as not to hijack this thread, in which I posed a couple of "normality" questions for 6G6-B owners that I would appreciate any input on if you guys get a chance.

Thanks, J.

(This message was last edited by jjj333 at 02:36 PM, Feb 28th, 2006)

Next 20 Messages  

FDP Forum / Fender Amps: Vintage (before 1985) / 6G6-B owners: Do ur bass controls respond & what up w/norm. chan. treb.?




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