Hello all.
Has anyone know of a schematic that uses DAF 91,DL94,DK92,Df91 or some of them for a guitar amp.
I have a Roberts CR portable mains powered radio that I would like to convert
Thamks
Has anyone know of a schematic that uses DAF 91,DL94,DK92,Df91 or some of them for a guitar amp.
I have a Roberts CR portable mains powered radio that I would like to convert
Thamks
Enter each type into google. I suggest the radio museum site for each data sheet.
None have common specs. The heaters are all like 1.4v or similar. One of the tubes is a low power power tube, enough to drive a small speaker at not loud volumes. The other tubes are all really RF tubes. One is a pentagrid converter, the others are lentode or pentode/diode types.
As to the radio itself, does it have a power transformer? If not, don't even consider the project without adding an isolation transformer.
None have common specs. The heaters are all like 1.4v or similar. One of the tubes is a low power power tube, enough to drive a small speaker at not loud volumes. The other tubes are all really RF tubes. One is a pentagrid converter, the others are lentode or pentode/diode types.
As to the radio itself, does it have a power transformer? If not, don't even consider the project without adding an isolation transformer.
Well then, the little power tube is probably already wired up to a tiny output transformer, so you could likely keep the power amp stage. As to using the pentodes as gain stages for guitar, who knows, you can try. Pentodes have high gain, but it might be possible to strap one's extra grids to the plate and use like a triode. Might work, might not. Can't lose.
And I couldn't tell you specifics, but there are some low voltage tubes of more useful type - like triodes - out there in the world of old tubes. Might find one of those.
Actually one pentode mught be OK. Look at the original Fender Champ 5C1.
And I couldn't tell you specifics, but there are some low voltage tubes of more useful type - like triodes - out there in the world of old tubes. Might find one of those.
Actually one pentode mught be OK. Look at the original Fender Champ 5C1.
Pretty simple, just go in on the top of the volume control - and see how much gain you get. I don't recall there ever been Roberts valve portables (or Roberts valve radios at all?), perhaps they were pretty rare beasts?. I repaired lot's of Roberts radios 'back in the day', but they were always the poor mans Hacker 😀
However, I wouldn't expect much power out of such a tiny amplifier.
> guitar amp. ..... Roberts CR portable mains powered radio that I would like to convert
1) Is it safe?? Most post-WWII domestic mains tube radios were HOT CHASSIS. This is safe as long as you can not touch the circuits (all wood/plastic case, radio waves in, sound waves out). A guitarist holds a wire to the circuit all the time s/he plays. DANGEROUS.
In this case, the Roberts BR *does* have full transformer isolation, as you already stated. But you always want a second pair of eyes just to be sure.
2) are your expectations realistic? Home radios are moderately loud in a home. Battery radios are less-loud to get useful battery life. The DL94 makes less than 1/3rd Watt semi-clean audio output. It won't fill Wembley Stadium or out-shout a drummer. But it is frequently reported here that a 1/4W guitar rig is VERY LOUD in an average home.
Any radio is a radio tuner and an audio amplifier. There is NO reason to tear it apart! Replace the tuner feed with a guitar jack. As said, go in the top of the Volume pot.
Sensitivity at radio volume pot is usually 50mV-100mV. A classic guitar amp is around 20mV. Modern guitars can easily deliver >100mV, so you get the whole part-Watt you bought. If it seems like hard work to slam the poor DL94, add some kind of booster-pedal in front. You could alternatively re-wire the IF tube as a preamp stage, but it is a lot of work for the small benefit.
1) Is it safe?? Most post-WWII domestic mains tube radios were HOT CHASSIS. This is safe as long as you can not touch the circuits (all wood/plastic case, radio waves in, sound waves out). A guitarist holds a wire to the circuit all the time s/he plays. DANGEROUS.
In this case, the Roberts BR *does* have full transformer isolation, as you already stated. But you always want a second pair of eyes just to be sure.
2) are your expectations realistic? Home radios are moderately loud in a home. Battery radios are less-loud to get useful battery life. The DL94 makes less than 1/3rd Watt semi-clean audio output. It won't fill Wembley Stadium or out-shout a drummer. But it is frequently reported here that a 1/4W guitar rig is VERY LOUD in an average home.
Any radio is a radio tuner and an audio amplifier. There is NO reason to tear it apart! Replace the tuner feed with a guitar jack. As said, go in the top of the Volume pot.
Sensitivity at radio volume pot is usually 50mV-100mV. A classic guitar amp is around 20mV. Modern guitars can easily deliver >100mV, so you get the whole part-Watt you bought. If it seems like hard work to slam the poor DL94, add some kind of booster-pedal in front. You could alternatively re-wire the IF tube as a preamp stage, but it is a lot of work for the small benefit.
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Thanks all. The tuner section only just picks up 2 stations and i like a low power amp, It uses a selenium rectifier and I would like to change diodes and I know I would need to add a resistor to keep the ht below 90v,anyone an idea of value ,thanks