Questions for a first build

Pat_rocks92

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Hello, i'm going to build my first amp a micro bassman based on rob robinette :


My first question is about mustard capacitors those have a 450v value indicated on the website but will it be fine to go with 400v ? (i ordered some vintage mullard mustard caps). Here are some Volt readings at the end of the page : https://robrobinette.com/Bassman_Micro.htm



My second question is there anyone kind enough to make a layout of this battery tube amp which sounds extremely good :



Schematic :

Does it need any transformer or choke ? if yes what should i take ?

commentary :

Battery Valve Guitar Amplifier. Presented here is an all valve battery powered guitar amplifier schematic. If a guitarist wishes to have a classic valve sound and desires it to be battery powered, the schematic here is apt. Output is only 0.2 watt, or 200mW, so isn’t very loud. It’s suggested that a high sensitivity speaker is used. Most of the components are inside a Vidor Lady Margaret Radio, or similar type, common in the 50s. They appear on eBay frequently at the time of writing, although it would be a shame to scrap a pristine example. One of these radios has the DL and DAF valve types but an additional DAF94/6 is needed. Three stages of amplification are required to effectively be driven from most electric guitars. It should also be stressed that a clean undistorted sound would only be possible through a low volume setting, but as valves are usually chosen for their distortion characteristics, it’s assumed the guitarist wants this. The battery is built by arranging 10 of the 9 volt smoke alarm batteries that at the time of writing are available for 50 pence each from £ Land. The LT battery can be any 1.5 volt AAA, AA, C or D cell, commonly available.
 

dan40

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If you are using a power transformer that could put out over 400v, going with higher voltage caps would be wise. Whenever you power up an amp without the tubes installed, such as doing the first startup or troubleshooting, the B+ in the amp will rise to a much higher level. Having caps with a bit of extra voltage rating is wise. I will say that many old Marshall amps used 400v Mustard caps for many years and some of them can go over 500v with or without tubes.
 

2L man

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That chematic has so low count of component that you can use for example Champ board. There is no need to have a "layout" because it is very easy to use the schematic for amp building. Just print schematic and mark all component legs, tube sockets, wires when you put them together and then make circle over the dot when you solder it! Then it is done ready and You know it is done!!! This is how electric technicians are teached to work and it becomes a document which your possible future customers appreciate. Measure also resistors values and write them to same print because they do have a tolerance and you don't need to trust only color bands and if your multimeter can measure capacitance measure capacitors too.

No need to use Choke for a battery operated amp!

It looks like power tube is fixed biased but does not say what is the voltage? Perhaps last one of the ten series connect 9V batterys is used for bias and cathode go to its positive? I would use cathode biasing like most SE quitar amps do! Obviously filament voltage is 1,5V and for that bigger cell battery is needed of few smallel parallel?
 
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andrewRneumann

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If you are using a power transformer that could put out over 400v, going with higher voltage caps would be wise. Whenever you power up an amp without the tubes installed, such as doing the first startup or troubleshooting, the B+ in the amp will rise to a much higher level. Having caps with a bit of extra voltage rating is wise. I will say that many old Marshall amps used 400v Mustard caps for many years and some of them can go over 500v with or without tubes.

There are many different versions of this amp. The main concern is the unloaded voltage of the PT. The Hammond 270AX lists 274vac for a peak voltage of 387V. That’s pretty close to 400V. Sometimes the wall voltage can change and push you even higher. If you can build one of the versions with a lower voltage PT, you‘ll be safer. Good luck!
 




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