Tube Radio Guitar Amp: Part 4 Pacemaker tagboard layout

There are few interesting videos of tube radio guitar amps conversions on the web.  All of them however, are single-ended amplifiers, i.e. using only one power tube (like the Fender Champ).  As far as real conversions go, this is about the only video that’s relevant:

Just using the phono input to plug in your guitar is easy, here’s an instructional video if you need that:

The silly dilemma in the second video sums up the reason why there is so little information on the web about conversions:

  • If you want, you can play guitar on any tube radio with a phone input, you just need a connector cord.
  • To make an optimum guitar amp out of the tube radio components, you will have to completely rebuild it, so you can win some of the power the previously went to the RF section tubes for your amp. If the radio was a stereo unit, you want to use the power available for a mono channel.

So it’s either use as is or rebuild completely, there is no middle road or easy guide. In fact, when cheap generic strattera online no rx buying a tube radio set, keep the following pointer in mind:

  • the more tubes, the better
  • more channels is better (stereo is twice the power)
  • the bigger the power transformer, the better
  • look for radios with ECC83 (preamp) EL84 (power) and EZ81 (rectifier)
  • avoid radios from the 40’s
  • bigger speakers is better, better change that the output transformer(s) can be used

On the other hand, I have not seen a tube radio that does not contain all elements of a 5W Champ head: often tubes, sockets, chassis, mains transformer, terminal strips and components can be salvaged.  This leaves you only with the cost of a very good output transformer for 5W single ended amp (40 euro max), some jacks, a pilot light and pots, just to build your own 5W monster (with vintage power transformer :-p)

So, there was work at the drawing board…

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And the vibrato section:

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Looking for the right components:

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The bloodsucker from the amp parts store charge 25 euros for a Tweed Deluxe tagboard, which is just a stupid piece of cardboard.  In the GAMMA store I found this riveting set for 11 euros.  The rings are a bit larger than normal tagboards, but work just fine.

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Laying out the board:

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Tremelo board and main circuit board wired up:
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Tube Radio Guitar Amp: Part 3 Making Plans – Vox Pacemaker 1965

Yes, there is a very nice and decent guitar amp hidden inside this scruffy old Philips radio, all the components except a suitable output transformer and speaker are present to solder up this nice gem:

Huh? Why? How?

Power rectifier EZ81 — If you are in Europe and hunting for tube radio with any value in the guitar amp field, check for this rectifier tube. If you see it, buy the radio!  This tube is used is the early Vox amp, up to the AC15 as power rectifier.  Most vintage American amp you will be looking at require at least 3 different voltage from the transformers: a high voltage, 6.3V for the tube filaments and 5V for the rectifier. The EZ81 does not require the special 5V, just feeds off the high voltage.

phillipspowersectionIn this way, it is just like a Vox Pacemaker — although below schematic is from a Cambridge Reverb (the same amp + reverb):cambridgereverbpower

Or an AC-15, also using an EZ81:

ac15_detail

And all of these are unlike any 50’s Fender amp, which require three voltages on the transformer 6.3V, HV and 5V especially for the rectifier:

5e3_rectifier
Transformer and rectifier tube in a Fender 5E3 Tweed Deluxe amplifier.

2 Power tubes EL84 & 1 Preamp tube ECC83 — if the transformer can power this in our radio, we need only one extra ECC83 tube to make a Vox Pacemaker. It uses 2 x EL84, 2 x ECC83 and an EZ81.  The Philips radio powers and additional 5 tubes for RF purposes, so it is certain that this transformer from a piece of €10 junk can function as the heart of a Vox Pacemaker, Vox AC-15 or Marshall 18W…. value: $75. My calculation seems to indicate this transformer could pull 5.4A on the high voltage.  I don’t believe you could find one that would feed anything more than a 25W amp.

Voxpacemaker_corrected

The only thing that is missing, is the output transformer, which will cost around €50. Chassis, resistors (after measuring), 6.3V pilot light and mounting screw can all be salvage from the zombie corpse.

I really think you could use a lot of the power transformers in old radios, but the output transformers from household radio sets will never be strong enough.