09-05-2018, 09:06 AM
Lovely sets. It's fair to say that I've done a few of these over the years. Yes, tuner comes from Görler for both the RV14 and RV20. It's hard to tell them apart externally, but the earlier model used in the RV14 lacks AFC. The later model can be extended to a little over 106MHz if you don't mind the scale indications being inaccurate. There's only a little bit of warm-up drift with the RV14, but the RV20 shouldn't have any at all if the AFC is working.
Apart from the usual problems of caps in the audio stages, the next most common problem with these is the metal rectifier. The original can be taken apart and "re-stuffed" with 4 IN4007 diodes and a 47 ohm ceramic WW resistor if feeling keen; otherwise there's plenty of space to mount a rectifier and resistor under the chassis. The main smoothing block is somewhat reliable; I end up leaving about half of them in place, but they are easy to re-stuff if desired (or modern replacements can be found). Sometimes the other smoothing cap plays up, but I've never bothered re-stuffing those as there's plenty of space in that part of the set to install a couple of axial capacitors.
I routinely replace most/all of the resistors in the audio stages. Once I did a step-by-step procedure, measuring the effect on power output and distortion of each replacement, just to convince myself of the value of what I was doing. I wish I'd written up my notes at the time, but suffice to say I was personally convinced of this - though I fully accept that many others would prefer to be "sympathetic" in their restorations.
Away from there though, I always replace the 15k resistors in the discriminator, as that makes quite a difference to the distortion performance. And C25 and C26, naturally.
R19 (1M) is always worth replacing, as that gets a bit more eye closure. R13 is often responsible for poor eye closure too. Not that yours lacks eye closure - from what I can tell from the video, it's the best example I've seen (usually, 5mm is as good as it gets). Yes, the 6k8 resistors are normally high, and I generally replace these with 2W carbon film resistors. I use 1W carbon film elsewhere. They look OK, but obviously are different to the originals. R41 (22k) is often worth changing, but I would guess that WW in that position might not be the best as it's the anode load for the osc/mixer stage. Other resistors are changed if more than 25% high, but I try to leave the IF stages alone as much as possible - they are not as easy to work on as the audio sections.
These sets always benefit from a full RF/IF lineup - that makes a huge difference in many cases. I've never tried a different front-end valve though - not that I have any ECC88s (but will look out for a couple - thanks for the tip!). Once fully restored, the sensitivity has always been pretty good with these sets.
I'd say the set sounded rather sibilant to my ears. Obviously the microphone might well play a part in this, but your voice sounded pretty natural to me (although I guess you were behind the mic?) In stock form, these sets don't lack HF, but I'm still a bit over-sensitive to bright sounds - no doubt that will change as I get older. Some people feel that these sets have a touch too much mid-range - I did help a chap on UKVRRR to get his set sound more like a stereotypical German "woody" by adding a filter to reduce the midrange. The way we implemented that was very neat - it took the signal from the tape output and put it back in via the gram input - this obviously means no internal modifications, as it was just a tiny "project box" with a couple of short wires with the phono plugs on. He was happy with the results, but while I could understand why, personally I preferred the way it sounded originally. Still, it's an easy way to modify the sound while keeping the set 100% original. I had the chance to hear what he'd settled on when he brought it here for an RF/IF line-up, which removed the mid-range "hardness" that was being caused by harmonic distortion from the discriminator.
Some might know that I've measured the acoustic output from a range of transistor sets, but I haven't got around to doing a Mayflower yet. Subjectively, I will say that it exceeded expectations, given that there's no equalisation built into the amplifier (which is the norm for decent transistor sets, of course), and the 5 by 8" version of that Goodmans speaker needs a lot of help from the EQ in the transistor sets. The version used in the Mayflower has a lot more HF than the smaller version, surprisingly.
Anyway, it's always good to hear that a set has made a new fan - I hope you enjoy yours as much as love mine
Apart from the usual problems of caps in the audio stages, the next most common problem with these is the metal rectifier. The original can be taken apart and "re-stuffed" with 4 IN4007 diodes and a 47 ohm ceramic WW resistor if feeling keen; otherwise there's plenty of space to mount a rectifier and resistor under the chassis. The main smoothing block is somewhat reliable; I end up leaving about half of them in place, but they are easy to re-stuff if desired (or modern replacements can be found). Sometimes the other smoothing cap plays up, but I've never bothered re-stuffing those as there's plenty of space in that part of the set to install a couple of axial capacitors.
I routinely replace most/all of the resistors in the audio stages. Once I did a step-by-step procedure, measuring the effect on power output and distortion of each replacement, just to convince myself of the value of what I was doing. I wish I'd written up my notes at the time, but suffice to say I was personally convinced of this - though I fully accept that many others would prefer to be "sympathetic" in their restorations.
Away from there though, I always replace the 15k resistors in the discriminator, as that makes quite a difference to the distortion performance. And C25 and C26, naturally.
R19 (1M) is always worth replacing, as that gets a bit more eye closure. R13 is often responsible for poor eye closure too. Not that yours lacks eye closure - from what I can tell from the video, it's the best example I've seen (usually, 5mm is as good as it gets). Yes, the 6k8 resistors are normally high, and I generally replace these with 2W carbon film resistors. I use 1W carbon film elsewhere. They look OK, but obviously are different to the originals. R41 (22k) is often worth changing, but I would guess that WW in that position might not be the best as it's the anode load for the osc/mixer stage. Other resistors are changed if more than 25% high, but I try to leave the IF stages alone as much as possible - they are not as easy to work on as the audio sections.
These sets always benefit from a full RF/IF lineup - that makes a huge difference in many cases. I've never tried a different front-end valve though - not that I have any ECC88s (but will look out for a couple - thanks for the tip!). Once fully restored, the sensitivity has always been pretty good with these sets.
I'd say the set sounded rather sibilant to my ears. Obviously the microphone might well play a part in this, but your voice sounded pretty natural to me (although I guess you were behind the mic?) In stock form, these sets don't lack HF, but I'm still a bit over-sensitive to bright sounds - no doubt that will change as I get older. Some people feel that these sets have a touch too much mid-range - I did help a chap on UKVRRR to get his set sound more like a stereotypical German "woody" by adding a filter to reduce the midrange. The way we implemented that was very neat - it took the signal from the tape output and put it back in via the gram input - this obviously means no internal modifications, as it was just a tiny "project box" with a couple of short wires with the phono plugs on. He was happy with the results, but while I could understand why, personally I preferred the way it sounded originally. Still, it's an easy way to modify the sound while keeping the set 100% original. I had the chance to hear what he'd settled on when he brought it here for an RF/IF line-up, which removed the mid-range "hardness" that was being caused by harmonic distortion from the discriminator.
Some might know that I've measured the acoustic output from a range of transistor sets, but I haven't got around to doing a Mayflower yet. Subjectively, I will say that it exceeded expectations, given that there's no equalisation built into the amplifier (which is the norm for decent transistor sets, of course), and the 5 by 8" version of that Goodmans speaker needs a lot of help from the EQ in the transistor sets. The version used in the Mayflower has a lot more HF than the smaller version, surprisingly.
Anyway, it's always good to hear that a set has made a new fan - I hope you enjoy yours as much as love mine
