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  1. chas.wahl

    Stompbox solid-state amp, and grounding

    I've been hankering to build one of those LM386-based amps* in a stompbox, but the whole thing about how to handle grounding mystifies me. For power, there are the (usual) built-in options to stick in a 9V battery, or to connect up to a power source with a 120>12V transformer, having filtering...
  2. chas.wahl

    5E3 input jacks (4) grounding

    I'm planning a 5E3 and using the "Merlin Blencowe" pragmatic modified star ground scheme generally, with a single bus for all in-amp components from power transformer secondaries to the (isolated from chassis) input(s), where the bus is connected to the chassis. My question is, with 2 (sorta)...
  3. chas.wahl

    Whither nickel-plated flat washers for Carling toggle switches

    On vintage (actually vintage) tweed amps, the Carling switches have thin flat washers beneath the face nut, like this: On recent builds you don't see them. They are not the anti-rotation keyed washers that are in Carling's current literature and sold by Mouser and TubesandMore.com, at least...
  4. chas.wahl

    Dylan sells out!

    Musically, it's another "date which will live in infamy" https://www.nytimes.com/2020/12/07/arts/music/bob-dylan-sells-publishing.html? Really? for $300 million? It's like the Dr Evil joke: "One Million Dollars . . ." It's only half a million per song. I can't believe it, and wonder what Jakob...
  5. chas.wahl

    Questions about Ampeg Reverberocket R-12-R reverb

    I'm having trouble understanding how the Ampeg R-12-R preamp works. It's a push-pull 6V6-based design with a paraphase phase inverter and all-octal tubeset, incorporating on-board tremolo and reverb. I'm pretty sure I get how the tremolo works: a triple RC network between anode and grid of the...
  6. chas.wahl

    Any difference between section 1 and 2 of a double triode?

    Perhaps a stupid question, but I've seen some schematics/layouts that use the higher-numbered anode/grid/cathode pins of a double triode as the "first" stage connected in a circuit. For example: And also advice to do the same: So, is this just a practical working out of wiring configuration...
  7. chas.wahl

    Input wiring puzzlement: Ampeg Reverberocket R-12-R 1962

    I have a new-found interest in this offbeat amplifier circuit, in its earliest of several variations. I'm busy investigating and learning more about how and why it's different from Fender circuits, but one thing has me stymied: how the inputs are wired. There are three inputs, labeled guitar...
  8. chas.wahl

    5F2-A: add screen resistor (470R) to 6V6, like Hoffman?

    The well-respected 5F2-A layout by Doug Hoffman adds a 470-ohm screen grid resistor connected to pin 4 of the 6V6. I've read discussion of these, to keep screen current from exceeding plate current, though I have not seen them on the Fender schematics I'm relatively familiar with for vintage...
  9. chas.wahl

    Tightening lock nuts of components inside chassis

    I've searched this and other sites, but haven't been able to find useful information about how one tightens the locknuts on "vintage" Fenderish components like jewel pilot lamp (13/16" or 21 mm) and fuse holder (11/16" or 17 mm); or standard-size switches (Carling 9/16" or 15 mm, NKK 14 mm or...
  10. chas.wahl

    3 tubes and 2 speakers in space: which configuration would you choose?

    5E3 cabinet with a simpler Class A amp in it, with a 10" and an 8" speaker on the baffle. There are four possible configurations in the elevation view, 2 shown; the other two are made by flipping the baffle on the y-axis -- but those would end up with the larger speaker magnet in close...
  11. chas.wahl

    Simplest practical B+ voltage dropper for low-power Class A amp

    The problem: have a dual-voltage secondary PT (275-0-275 or 325-0-325), and I'd like to have the option to use both, but lower the 325 to 300 (or thereabouts), for a Class A (single-ended) 5F2-sort of amp: only one 6V6, one 12AX7, using a vintage 5Y3GT rectifier. It seems to me that a single...
  12. chas.wahl

    5F2-A volume & tone pots: audio (log) or linear taper

    As I assemble parts for a 5F2-A (Tweed Princeton narrow panel) build, I am confused about the best taper to use for volume and tone control pots. Based on recent research: Vintage Fender schematic is non-specific, but their layout shows "LIN." for both volume and tone. Weber kit layout and...
  13. chas.wahl

    New cabinet day - Mergili unlacquered Tweed Deluxe

    For a DIY Tweed project, I did a bit of research, and decided to buy a standard Deluxe cabinet covered but unlacquered from John Mergili in Spokane. The price was a great value, it seems to me. From the time I made payment, it was only a week before it shipped, and I received it Thursday...
  14. chas.wahl

    Wire twisting for dual-voltage primary, dual-voltage secondary PT

    I'm building a project with a power transformer that has primaries wired for either 120 or 240 volt (wire them in parallel or series, respectively), and two different secondary HT voltages as well (again, 4 wires). It's a Hammond 290 CAX. I assume that since I'm planning to implement both...
  15. chas.wahl

    Output jack on front panel - problem?

    I'm building a little Class A amp head, with a variable resistor + knob to provide variable NFB. I've realized that the output jack and the NFB pot should be close to each other, to keep from having a wire or two passing cross-chassis. So, my choice is either to put them both on the front panel...
  16. chas.wahl

    Transformers: minimizing coupling

    In doing research for a fairly simple amp build, I've come across something that puzzles me. Please take a look at the following 4 items: From Merlin Blencowe's Designing Power Supplies for Tube Amplifiers (no longer in print, but available electronically through B&N, and in bits and...
  17. chas.wahl

    Switched dual-voltage power transformer?

    I'm going to build a 5F2-A clone, like about half the denizens of this subforum. I've been concerned about the "right" voltage to provide for B+ of the various stages. Based on my research, I suspect that a lot of folks don't pay that much attention to this when building this particular model...
  18. chas.wahl

    Fender CTS concentric pot anatomy

    This is the subject a stacked concentric pot with independent actuation of each. I'm building a Tele, but wanted to try separate tone and volume for each pickup, while still using the traditional T control plate and layout. I found that these were made, but I could only find them in...




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