Ferrograph Series Seven Speed Modification - UK Vintage Radio Repair and Restoration Discussion Forum

BennyCrossen · 20th Nov 2021, 10:29 pm

Hello all,

I've recently been rectifying a number of faults that were troubling my Ferrograph Series Seven M 713 machine.

As I was reading over the service manual, I noticed that the equalisation board between my model (713) and the high speed model (713H) isn't that drastic (except for a few differences in the ratings of capacitors and resistors that are used).

With this in mind, coupled with the fact that a TapeHeads forum member mentioned that the motor can be rewired for an increase in speed, at the expense of losing 1.875 ips (https://www.tapeheads.net/showthread.php?t=18776), I'm wondering if it's even feasible to carry out such a modifcation?

Would anyone be able to offer me advice or suggestions?

Thank You!

Radio Wrangler · 21st Nov 2021, 12:00 am

Increasing the speed of reel-reel recorders seems to be a very popular thing to do. There seems to be a lot of Revoxes floating around where the changes were rather bodged.

Before going ahead, are you really sure you want to do it? Unless you're recording from very good sources, like decent mikes, you're not going to notice much improvement at the top end. You will notice the increase in tape consumption.

What high speed does is also roll off your bass response somewhat more. It's a zero-gain game.

If you think of your replay head, it has a certain width of gap and it senses the flux variation over this length and that sets a high frequency rolloff that turns into a series of notched as it goes down.

Less well known, the pole pieces of the head have only a limited length on each side in contact with the tape. THe head senses the flux average on each side and responds to their difference. This sets a similar roll-off effect on the low frequency end of the response.

Consequently, the pole-length-of-contact/gap-length ratio of a head sets how many octaves it can cover. Changing the tape speed maps where in the audio spectrum these octaves lie. You can't win at one end without losing at the other. Machines designed from the outset to handle 15ips have long pole pieces in large heads and go to lengths to wrap the tape around them for good length of contact.

Unless you have some tapes already recorded at 15ips which you want to play, you need to find out if the Ferrograph heads were designed with long pole contact.

David

BennyCrossen · 21st Nov 2021, 12:05 am

Thank you for your quick reply.

I'm not aware if the higher speed models used different heads. I will have to conduct further research.

On the topic of tape consumption, it really doesn't bother me.

Based on your advice, I'm beginning to see that a modifcation such as this can have a wide range of effects on the machine.

I will certainly have to think about this, but, thank you for your advice.

Benny

TIMTAPE · 21st Nov 2021, 2:04 pm

Another obvious downside is that tape heads wear down twice as fast. As it is, this machine and earlier Ferro's had comparatively short head life because the manufacturer stayed with felt pressure pads which were brutal on heads. Back in the day, spare new heads were easily obtained but no longer.

BennyCrossen · 21st Nov 2021, 2:45 pm

Is there anyway to mitigate the head wear caused by the presence of the felt pads?

Benny

Ted Kendall · 21st Nov 2021, 3:42 pm

Let the poor thing be - it's half track mono to start with, it won't work properly without pressure pads because of the tape path layout, and you're going to have to sleeve the capstan to do a high speed conversion. If you want to experiment with high tape speeds, I'd get an A77 or a high speed Ferro, if you prefer.

BillDWVA · 23rd Nov 2021, 5:01 pm

Quote:

Originally Posted by BennyCrossen

With this in mind, coupled with the fact that a TapeHeads forum member mentioned that the motor can be rewired for an increase in speed, at the expense of losing 1.875 ips (https://www.tapeheads.net/showthread.php?t=18776), I'm wondering if it's even feasible to carry out such a modifcation?

Would anyone be able to offer me advice or suggestions?

Thank You!

Hi, I think you may find that the difference in the capstan motor is only the diameter of the stepped hub on its shaft that contacts the idlers and transfers drive to the capstan flywheel. I.e. the motor runs at the same rpm on all models. However this may need to be double-checked. My 704 has the same three speeds.

It will not work without pressure pads and that is a cross all early Ferrograph enthusiasts have to bear. Look out for good spare heads and keep a stock. One can mitigate some of the wear by removing the tape from its normal path during fast winding.

As others have stated it may be better just to find a high-speed version to replace or supplement yours?

Bill

BennyCrossen · 23rd Nov 2021, 7:26 pm

I'm glad you have all talked some sense into me. Some ideas should just never be uttered.

I will keep my eye out for a high speed model.

Following my cleanup of the tape path and of the fuse holders, I've ran into a problem: any sound (whether it be it from an input or from a tape) is incredibly quiet and distorted. I've followed chriswood1900's advice from a previous thread, in which he mentions that a troublesome electrolytic capacitor is to blame (https://www.vintage-radio.net/forum/...d.php?t=149249), and I've replaced it. However, the issue still remains.

Should I perform a recap of the aforementioned board? Any pointers?

Many Thanks,
Benny.

20th Nov 2021, 10:29 pm	#1
BennyCrossen Diode Join Date: Oct 2019 Location: Newton Aycliffe, County Durham, UK. Posts: 4	Ferrograph Series Seven Speed Modification Hello all, I've recently been rectifying a number of faults that were troubling my Ferrograph Series Seven M 713 machine. As I was reading over the service manual, I noticed that the equalisation board between my model (713) and the high speed model (713H) isn't that drastic (except for a few differences in the ratings of capacitors and resistors that are used). With this in mind, coupled with the fact that a TapeHeads forum member mentioned that the motor can be rewired for an increase in speed, at the expense of losing 1.875 ips (https://www.tapeheads.net/showthread.php?t=18776), I'm wondering if it's even feasible to carry out such a modifcation? Would anyone be able to offer me advice or suggestions? Thank You!

21st Nov 2021, 12:00 am	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,858	Re: Ferrograph Series Seven Speed Modification Increasing the speed of reel-reel recorders seems to be a very popular thing to do. There seems to be a lot of Revoxes floating around where the changes were rather bodged. Before going ahead, are you really sure you want to do it? Unless you're recording from very good sources, like decent mikes, you're not going to notice much improvement at the top end. You will notice the increase in tape consumption. What high speed does is also roll off your bass response somewhat more. It's a zero-gain game. If you think of your replay head, it has a certain width of gap and it senses the flux variation over this length and that sets a high frequency rolloff that turns into a series of notched as it goes down. Less well known, the pole pieces of the head have only a limited length on each side in contact with the tape. THe head senses the flux average on each side and responds to their difference. This sets a similar roll-off effect on the low frequency end of the response. Consequently, the pole-length-of-contact/gap-length ratio of a head sets how many octaves it can cover. Changing the tape speed maps where in the audio spectrum these octaves lie. You can't win at one end without losing at the other. Machines designed from the outset to handle 15ips have long pole pieces in large heads and go to lengths to wrap the tape around them for good length of contact. Unless you have some tapes already recorded at 15ips which you want to play, you need to find out if the Ferrograph heads were designed with long pole contact. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

21st Nov 2021, 12:05 am	#3
BennyCrossen Diode Join Date: Oct 2019 Location: Newton Aycliffe, County Durham, UK. Posts: 4	Re: Ferrograph Series Seven Speed Modification Thank you for your quick reply. I'm not aware if the higher speed models used different heads. I will have to conduct further research. On the topic of tape consumption, it really doesn't bother me. Based on your advice, I'm beginning to see that a modifcation such as this can have a wide range of effects on the machine. I will certainly have to think about this, but, thank you for your advice. Benny

21st Nov 2021, 2:04 pm	#4
TIMTAPE Octode Join Date: Jul 2006 Location: Perth, Western Australia Posts: 1,969	Re: Ferrograph Series Seven Speed Modification Another obvious downside is that tape heads wear down twice as fast. As it is, this machine and earlier Ferro's had comparatively short head life because the manufacturer stayed with felt pressure pads which were brutal on heads. Back in the day, spare new heads were easily obtained but no longer.

21st Nov 2021, 2:45 pm	#5
BennyCrossen Diode Join Date: Oct 2019 Location: Newton Aycliffe, County Durham, UK. Posts: 4	Re: Ferrograph Series Seven Speed Modification Is there anyway to mitigate the head wear caused by the presence of the felt pads? Benny

21st Nov 2021, 3:42 pm	#6
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Re: Ferrograph Series Seven Speed Modification Let the poor thing be - it's half track mono to start with, it won't work properly without pressure pads because of the tape path layout, and you're going to have to sleeve the capstan to do a high speed conversion. If you want to experiment with high tape speeds, I'd get an A77 or a high speed Ferro, if you prefer.

23rd Nov 2021, 7:26 pm	#8
BennyCrossen Diode Join Date: Oct 2019 Location: Newton Aycliffe, County Durham, UK. Posts: 4	Re: Ferrograph Series Seven Speed Modification I'm glad you have all talked some sense into me. Some ideas should just never be uttered. I will keep my eye out for a high speed model. Following my cleanup of the tape path and of the fuse holders, I've ran into a problem: any sound (whether it be it from an input or from a tape) is incredibly quiet and distorted. I've followed chriswood1900's advice from a previous thread, in which he mentions that a troublesome electrolytic capacitor is to blame (https://www.vintage-radio.net/forum/...d.php?t=149249), and I've replaced it. However, the issue still remains. Should I perform a recap of the aforementioned board? Any pointers? Many Thanks, Benny.