Recent Posts

91

Tube Amp Building - Tweaks - Repairs / Re: silvertone 1484

« Last post by johnfromcyrene on June 02, 2026, 01:14:39 pm »

I believe you can also simulate sag with a resistor as well.

92

Other Topics / Re: Meme of the day

« Last post by shooter on June 02, 2026, 12:16:13 pm »

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93

Tube Amp Building - Tweaks - Repairs / Re: silvertone 1484

« Last post by passaloutre on June 02, 2026, 10:33:24 am »

You can definitely use a tube rectifier to get more sag, but you'd be building yet a third different version of this power supply, so no one here can tell you what it will sound like. It won't be a 1484, but it may be something you like

94

Tube Amp Building - Tweaks - Repairs / Re: Bias Help for Rob Robinette JCM800 6V6

« Last post by sluckey on June 02, 2026, 05:53:01 am »

I've attached a simple bias adjust diagram. But I urge you to study Rob's schematic because it allows you to adjust the bias level as well as balance the bias between the two output tubes. BTW, there is only one trimmer mounted on the big pot.

95

Effects / Re: Jfet based on board guitar booster

« Last post by TIMBO on June 02, 2026, 04:54:53 am »

Thanks mate.
Found a couple of BC547 transistors in my junk box and found this..
ggg_geb_npn_sc.pdf
Will fit on a small piece of vero board

96

Tube Amp Building - Tweaks - Repairs / Bias Help for Rob Robinette JCM800 6V6

« Last post by rud85ny on June 02, 2026, 03:59:52 am »

Building a Rob Robinette JCM800 6V6 amp and Im stumped on the Bias layout that's depicted on the site. https://robrobinette.com/RR2104_Master_Volume_Micro.htm

I have a 25k potentiometer available, but I notice there are 2 trims wired to what looks like on top or side by side to one another?
Rob has a Trim and Balance adjustment for the bias. Is this necessary? Can I get away with just installing a bias voltage trim pot of 25kOhms?

I would be more than grateful if someone can draw out (in layman's terms) a bias layout for this amp.

97

Tube Amp Building - Tweaks - Repairs / Re: silvertone 1484

« Last post by johnfromcyrene on June 02, 2026, 01:41:22 am »

I think the mojotone uses diodes instead of a rectifier. what about adding a gz34 to create sag for the amp?

98

Tube Amp Building - Tweaks - Repairs / Re: Ampeg SB-12 inspired amp

« Last post by Banjan73 on June 02, 2026, 12:26:27 am »

Ok.
After all the measurements in the Oscilloscope thread, heres the updated schematics.
One of the nearest day, I will adjust bias a little bit warmer while I run a signal and check with the scope if those spikes vanishes. If not, maybe I will go further down on those coupling capacitors before the EL34s. Some say 22nF is better? But then I`ll have to order some. Don`t have 22nF with an acceptable voltage rating.
Maybe, for safety of my OT, I will go up a bit on R27 on the PS to lower the screen a little bit. But all these are thoughts I have. Any thoughts here?
And yeah, I know I should make more measurements. Just a little lazy, and since I don`t have a permanent work shop, I must each time connect all the instruments (I am working at our living room table).

99

Tube Amp Building - Tweaks - Repairs / Re: silvertone 1484

« Last post by passaloutre on June 01, 2026, 11:21:51 am »

which one sounds better then?

Well that's pretty subjective. I may be one of the few who've played both, and I'd say they both sound great. The "tone" is quite similar, as the preamp hasn't changed, while the changes to the power supply affect more the "feel" of the amp. I would say the Silvertone has a spongier, compressed feel with less headroom, and the Mojotone version is more punchy and dynamic, loud.

It was my first amp build, so I followed Mojotone's circuit faithfully. Knowing more now, many years later, the Mojotone design almost seems a step between the original Silvertone and something like a 1970s Orange amp: https://el34world.com/charts/Schematics/files/Orange/Orange_graphic_mkii_or120.pdf, the chief difference being negative feedback.

100

Other Topics / Re: Meme of the day

« Last post by shooter on June 01, 2026, 10:47:48 am »

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