Amp advice.

chas.wahl

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Believe it or not, 5 watts is loud as well
Amen to that; 1 watt can be too loud!

Attenuator:

Simple DIY (search for "10% Power" -- note that 10% power is only half the perceived volume)

More sophisticated DIY
I suggest the M2 shown in the 1st post, without the stuff in red along the bottom if you don't need a 16 ohm connection; see post #539 on p. 27 -- note that this design will effect up to 31 dB reduction in discrete increments, or about 1/8 perceived volume, and if you don't need an attenuator that can handle a 50 W amp, you can reduce the wattage [and thus size] of the resistors -- will need to have a sign-in for the Marshall Forum to download anything or view images at larger size.

Commercial ($180 US) Nice but more pricey.

OR

Amp project with your favorite preamp design and low-power output tubes (EF80) -- search for "Micro Amps". There are build/discussion threads for many of these, both on TDPRI and other forums.

The nice thing about an attenuator is that it can be used with any amp it supports the ohmage and power of, so quieter for home, louder when you want that.
 
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Kev-wilson

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I do seem to be being drawn to RobRobinette's site if I'm honest and his 1 watt Micro Deluxe, I'd say there is enough info there (and photos) for a guy with some practical skills to stand a fair chance of building an amp without blowing anything up :) (once I dig where I get the 250-0-250 transformer for SS rectification from in the UK and I've more theory to absorb)

It's funny as he shows a head made from what appears to be 'Zebrawood' and I'd been pricing planks of it anyway :) as now I've done some box joints I could do some more...
 

Kev-wilson

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The handles must arrive this week (said in a hopeful voice) so I've been busy reading, I've also got a new jack lead to continuity test pick ups (I just wanted some soldering practice as I don't need the lead 😁) as a lead into a first attempt at a RobRobinette Deluxe Micro in the coming months once I've learned a little more about theory, I can find an output transformer but am a little confused by power transformers so far.
1653817573987.png

So a question if I may, the above tranny, can an artificial centre tap be added on the board to take 250v from each secondary? I don't think it can but need to ask as I'll not learn if I don't ask :)
 

chas.wahl

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I'm not sure what question you're asking, so I'll attempt an answer that might be off-target. A power transformer for a guitar generally either has a center tap for the HT secondary, or doesn't, and adding a center tap to one that doesn't have one would mean (I'm fairly certain) rewinding it.

For example, take a look at @robrob's "Deluxe Micro" page, where designs are shown using either a single 12AU7 (dual triode) or a pair of EF80 (pentode) tubes for the low-power output tubes. The micro designs generally follow a methodology of grafting a vintage standard preamp section (with largely similar voltages to the original design) onto a power section with somewhat lower, or at least "adjusted" voltages to suit the lower-power output tubes (lower or no dropping resistors for power section).

If you look at the Deluxe Micro designs, the 12AU7 variants seem to be using a power transformer with a 275-0-275 HT secondary (550 VAC with a center tap), while the EF80 version (search for "Deluxe Micro EF80") uses the popular AnTek AS05T200 toroidal that doesn't have a center tap and has a 200 VAC secondary. The design without a center tap has a somewhat different wiring, and uses a diode bridge rectifier rather than a vacuum tube rectifier to address this. As pointed out in @King Fan's recent thread about a Bassman Micro build, AnTek also has a higher-output 240 V version, if that's what you want.

Does that help, or have I missed the point?
Edited again, because OP was talking about a Deluxe Micro build, not Bassman; my apologies.
 
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King Fan

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Yes, on early builds, it’s best to build from the standard suggested parts, especially PT and OT. We have a good number of micro amp builders in the UK and EU who may be able to advise — and check out all the Deluxe Micro build and plan threads you can find. I don’t know if Antek ships across the pond, but toroids in general are more common east of it.
 

Kev-wilson

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I think chas.wahl nailed it with "I'm not sure what question you're asking" :) as I'm not sure what I'm asking either :) I guess like many I'm preparing to jump in so am asking questions/waffling about things I've yet to learn... The center tap question came from confusing full wave rectification with a full wave bridge rectifier, as the latter mentioned a center tap (I think I read that) and with reading the solid state rectification sweet spot was 250 - 0 -250 for the deluxe micro I have been looking for a UK supplied tranny as an alternative to the Hammond or ClassicTone mentioned, and was looking at a site recommended by a UK kit maker who make his Champ clone trannys.

I was going to buy the WF55 kit but 5 watts will be too much loud for home (I do know where the volume control is btw :p 😀 ), and as my current amp is a British sounding one the next should be 'American' sounding, I have a mates Champ 600 at mine which is nice, but again it's at its best loud and not mine so the Delux Micro RobRobinette looks like it want me to have a go at building it.

Which is easier said than done :) as I have all the parts to source and my first foray into buying cabinet parts has been frustrating but the handles may come this week:rolleyes: (and if I keep saying it it'll come true), I can source plate for a chassis and bits to make a turret board with but haven't bought a resistor since the local Maplins shut...
 

andrewRneumann

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The handles must arrive this week (said in a hopeful voice) so I've been busy reading, I've also got a new jack lead to continuity test pick ups (I just wanted some soldering practice as I don't need the lead 😁) as a lead into a first attempt at a RobRobinette Deluxe Micro in the coming months once I've learned a little more about theory, I can find an output transformer but am a little confused by power transformers so far.
View attachment 988371
So a question if I may, the above tranny, can an artificial centre tap be added on the board to take 250v from each secondary? I don't think it can but need to ask as I'll not learn if I don't ask :)

I would use the first one with a bridge rectifier. If you want to use a tube rectifier, use a couple of solid state diodes to create one half of the bridge. I prefer this over the second PT you suggested because the current handling of the first one is better. Center-tapped PT's are less efficient and require heavier windings because they create more ripple current in each half of the secondary. OMMV.
 

chas.wahl

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If you want to test out, in a preliminary way, what a circuit's B+ voltage is likely to be with a given transformer, SE or PP design, power tube wattage and number of preamp tubes (with optional output transformer impedance for resistive load) you can check this calculator out:

The only possible hitch is that for "non-standard" power transformer voltages, it allows a single custom voltage value to be entered, which is interpreted as ###-0-###. This may mean that it assumes the secondary is center-tapped. Whether that makes a difference, I don't have the technical know-how to tell. As @King Fan has said, for newbies like us maybe it's best to stick with a published or proven design rather than improvising.

Also, it would have been good to note that the two PTs you included schematics of were by Ampmaker, and what their specs were. If you go to @King Fan's Micro Bassman thread I linked-to above, one @Hyakuya from your side of the pond appears to have used one of them for a couple of micro amps, and could give you some advice. A "hybrid bridge" is mentioned, though not described further than that.
 
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Kev-wilson

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If you want to test out, in a preliminary way, what a circuit's B+ voltage is likely to be with a given transformer, SE or PP design, power tube wattage and number of preamp tubes (with optional output transformer impedance for resistive load) you can check this calculator out:

The only possible hitch is that for "non-standard" power transformer voltages, it allows a single custom voltage value to be entered, which is interpreted as ###-0-###. This may mean that it assumes the secondary is center-tapped. Whether that makes a difference, I don't have the technical know-how to tell. As @King Fan has said, for newbies like us maybe it's best to stick with a published or proven design rather than improvising.

Also, it would have been good to note that the two PTs you included schematics of were by Ampmaker, and what their specs were. If you go to @King Fan's Micro Bassman thread I linked-to above, one @Hyakuya from your side of the pond appears to have used one of them for a couple of micro amps, and could give you some advice. A "hybrid bridge" is mentioned, though not described further than that.
Thanks for the heads up :) I was wary posting links to 'commercial' folk as I don't know what the rules are, but yes, it's a windings site Ampmaker uses for his kits and links to, so I was looking to see if there was something with 250 - 0 -250 & 6.3v secondarys with ss rectification instead of a tube, so wouldn't need the 5v tap, I'll have a read of the thread you mention but do think the 2nd one I posted could be ok (but am happy to be disabused).

If it's metal or wood and going to waste I'd always ask if I could look to repurpose it and often find myself buying 'this' to make 'that' from which are traits best avoided looking at building an amp...
 

Len058

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I don't know if you have to pay import tax getting stuff from the EU but this PT worked in my Champ and Bassman micro's.

https://www.tube-town.net/ttstore/toroidal-30va-8808.html It had the Antek voltages

If you really want 250V

 

Kev-wilson

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When I read 'toroidal' I shuddered :) simply as they're a different shape to what I've been looking at and reading up on, I watched the Uncle Doug video last night on power transformers again too, if I used a rectifier valve I could use the Hammond pt specified for the build but would prefer solid state which is 25v a side less, so could use dropping resistors if I worked the maths out and shielded the 5v secondary. (or so I think)

I'll read about toroidal transformers this evening :) and I got an email letting me know my handles were posted today :)
 

Len058

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Tordoidal are cheaper and the current doesn't care. If you're doing a SS rectifier, why not?

I would build a cheap champ first, just to learn and to try. If the bug hits you, you can spend your money on a Blackvibe, Deluxe or Bassman.
 

King Fan

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My limited understanding is toroidal may be cheaper, lighter, and quieter. Many users, especially overseas, will know more. My limited experience suggests they can be harder to mount on a chassis with a standard PT cutout and may take up a bit more horizontal space. They may be considered ugly if open to view. There may be other downsides, but….
 

Kev-wilson

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Tordoidal are cheaper and the current doesn't care. If you're doing a SS rectifier, why not?

I would build a cheap champ first, just to learn and to try. If the bug hits you, you can spend your money on a Blackvibe, Deluxe or Bassman.
Ah, it's the Micro Deluxe I want to build, just 1 watt output, and the 2 extra dials have swung me that way instead of the Micro Champ also shown on the RobRobinette site.

My limited understanding is toroidal may be cheaper, lighter, and quieter. Many users, especially overseas, will know more. My limited experience suggests they can be harder to mount on a chassis with a standard PT cutout and may take up a bit more horizontal space. They may be considered ugly if open to view. There may be other downsides, but….
Instinctively I don't like the shape but will read up on them (and chokes) as I've a lot to learn.
Edit, I re read the RobRobinette micro build page again properly, did a google search for the PT mentioned and found an equivalent on the site I linked to above, which is a relief 🙂
 
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Kev-wilson

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I’m pleased with that, the finger joints would have been easier in pine but at least the oak gave my Kity K5 a good test and finished suits my living room which is pleasing :) and I've enough oak left to make a head unit for a 1 watt Deluxe Micro :p as the Night Train clone there although nice sounding is a little loud.

I see why a kit is a good starting point as sourcing the necessary parts is going to be quite tedious, but then again I'm learning whilst I'm looking and trying to decide on eyelet, tag or turret board...
 

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Kev-wilson

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A few days down the road and my transformer confusion is less than what it was :) or I dig RMS and peak voltage after smoothing a little more now courtesy of Uncle Doug on YouTube and am more confident I can choose the right one, or one that'll work with the 'justification' for choosing it.

Not yet though, as I've all the parts to source and that'll be a mission as nowhere here in the UK sells everything under one roof, I see a Hammond chassis (1444 18) that's bigger than needed but will give me more room to work in, I need to make up my mind as to turret or tag board next :)
 

Kev-wilson

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I think (I've mates who'll dispute that :p ) I'm going to try a 250-0-250 PT as recommended on the website, the Luddite in me wants the 'square' shaped one too :)
1654705259873.png

This the one I think will work in the Deluxe Micro with solid state rectification, whether or not they've one in stock's another matter and there's a frame or clamp mount option, no drop through and not many options in the UK for that shape and size.
 




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