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Post subject: Re: 1968 Bassman
Posted: Sat Feb 15, 2014 10:31 pm
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Final fixes on reverted Bassman phase inverter and global feedback circuits.

New resistor nework on tail of phase inverter.


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Post subject: Re: 1968 Bassman
Posted: Sat Feb 15, 2014 10:35 pm
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Original AB165 layout for phase inverter and GFNB:


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Post subject: Re: 1968 Bassman
Posted: Sun Feb 16, 2014 1:58 am
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First fire-up. Very quiet amp. Think that those F&T caps with ww resistors in rail & the UF5408 diodes in rectifier bridge does make a difference. Biased RCA BP 6L6GC to 38 and 41mA at 474VDC and 473VDC respective plate voltages.

Now, to button up to cab and try out on Tremolux speaker cab. Will test versus blonde Tremolux head (AB763).

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Post subject: Re: 1968 Bassman
Posted: Sun Feb 16, 2014 2:49 am
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Ok... I'll try to sneak in some riffs, comparing the two heads (2:00am here). Mods were not exacatly easy. Tone is markedly browner than the stock AB165 --- both BASS and NORMAL channels. Much quieter background than before.

Mini review to follow. :mrgreen: :D :mrgreen:

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Post subject: Re: 1968 Bassman
Posted: Sun Feb 16, 2014 3:24 am
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Front and rear views:

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Post subject: Re: 1968 Bassman
Posted: Sun Feb 16, 2014 10:54 am
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Ok. Put the Bassman and Tremolux through some paces. The Bassman has a big tone. It's NORMAL channel has a more potent attack than the Tremolux's NORMAL channel. BASS channel is pretty crazy. I need to dial back the Les Paul's tone and volume. Can get an overwhelming feedback on command. Will try a 5751 in V1.

The two heads are a nice compliment. Tremolux has that nice tube rectified Bluesy tone and the Bassman has a distinct solid-state rectified attack. I have no bass guitar on hand, but I bet it would sound pretty good through this AA864 circuit.

Going through the 2 X 10-inch cab (two JBL K110) --- the Bassman is very loud. As loud as my SFSR with it's four 10-inchers.


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Post subject: Re: 1968 Bassman
Posted: Sun Feb 16, 2014 11:36 am
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Great job there Beemer! Thanks for giving us the tone reference too! 2:00AM testing? Man you are driven! Hope you kept those Blue Molded Tone Caps though!

T2

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Post subject: Re: 1968 Bassman
Posted: Sun Feb 16, 2014 1:12 pm
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Have you tried jumpering the channels on the modded Bassman yet?

Arjay

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Post subject: Re: 1968 Bassman
Posted: Sun Feb 16, 2014 9:42 pm
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Excellent, Beemer!!! I agree, those guys are very punchy with humbuckers. Art

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Post subject: Re: 1968 Bassman
Posted: Sun Feb 23, 2014 8:02 pm
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Steve, how's that bad-boy doin' ? Have you tried the 5751 in the V1 slot ? What about running it through a couple of 12's ? I've tried the 5751 in the V2 slot(not bad) and you know I tried 12AY7's in the V1 slot, until you told me I needed to adjust the surrounding components to accommodate that tube(yeah, toasted two of them, prior to your advice). But I really liked the 12AY7 input. I'll have to overcome my laziness and fix up that circuit!! Art

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Post subject: Re: 1968 Bassman
Posted: Mon Feb 24, 2014 12:08 am
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Art, the amp seems to be loosening up. Kinda tight sounding, at first. Lot more relaxed tone. Not to the level of the Tremolux. But closer. Still have awesome bass and bass-midrange. Best of any dual 6L6GC amp that I've tried. Very clean high notes.

Feedback is this crazy really slow, slow, SLOW winding-up like process. Like you can delay the complete onset by 30 seconds, just by moving the guitar back and forth from the amp. Something none of my other Fender amps seem to possess. I remember a vintage Bluesbreaker with KT-66's that had that kind of controlled feedback.

Gonna have that 2 X 12-inch cab made. Prolly one Vintage 30 and one 1962 Jensen P12N. We see how the amp sounds with that cab.

12AY7's are dead sensitive to plate voltages and cathode current parameters. You want them down in their linear range. Then, you get the full effect of tone, headroom, OD. Fender tied the cathodes together, in their early tweed iterations. Some ppl say that this has a lot to do with the channel interaction and overall tone of the famous Bassman 5F6-A.

http://www.webphix.com/schematic%20heav ... _schem.pdf


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Post subject: Re: 1968 Bassman
Posted: Thu Mar 06, 2014 2:35 pm
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Steve...make sure we get some pics of the head and cab together once you get the 2x12 built. You know how we love amp porn!

T2

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Post subject: Re: 1968 Bassman
Posted: Thu Mar 06, 2014 7:50 pm
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Will do! :D


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Post subject: Re: 1968 Bassman
Posted: Fri Mar 21, 2014 5:33 pm
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No ill will by posting in a present thread to hijack it, but I have a 68' Bassman that I would like to know what the particular circuit in it is.

I bought it without the cabinet so I had to make my own. I made it as a non standard Bassman box and I hope I don't piss someone off with the looks of it.

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The inside:

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Thank you in advance.


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Post subject: Re: 1968 Bassman
Posted: Fri Mar 21, 2014 6:05 pm
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Your amp began life as an AC568 but it looks like someone took it back to the AB165 revision, or at least partially so.

Why not start a new Bassman thread to avoid confusion?

Arjay

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