AVO HF135 - Setting RF Level Fault.... - UK Vintage Radio Repair and Restoration Discussion Forum

a_strong · 29th Jan 2018, 10:48 pm

I have recently purchased an AVO HF135 which is very clean and tidy but appears to have a fault on on of its ranges.

Although the Set RF Level control seems to work on other ranges I am unable to set it up properly on Range F, the 1-3MHz range. The attached photos may explain the problem.

The RF Level control is at minimum and Band F is selected.
The Function switch is set to CW.

At 1MHZ the reading on the RF Level meter is about 15% of FSD.
At 2MHz the reading on the RF Level meter is about 90% of FSD.
At 3MHz the reading on the RF Level meter is over 100% of FSD.

I would be interested to hear from anyone who might have experienced a similar problem on this or any other range or has any ideas about what may be causing this problem.

I have the original Operating Instructions but I have been unable to find any Servicing information anywhere.

Thanks in anticipation.

This effect is only on Range F and all other ranges behave as you might expect.

Freya · 30th Jan 2018, 9:29 am

Can't help with your problem but you may be interested to know this model is a re cased Taylor 68AM from when AVO took over Taylor Instruments.

karesz* · 30th Jan 2018, 10:15 am

HTML Code:

Although the Set RF Level control seems to work

Means it please that the real RF-output is correct or is varying in same character?
https://www.vintage-radio.net/forum/...ad.php?t=59275
I don't have an HF135, but I think that the solution is by search for contact problems in Fr.-range select switch (i.e. output coupling coil)-if the oscillator level itself is not so bad variing_can you check it with an oscilloscope please?

HamishBoxer · 30th Jan 2018, 12:53 pm

I have the HF135 and mine seems to be similar on range F.There is a fair degree of o/put variation on that range.

a_strong · 30th Jan 2018, 5:09 pm

Thanks very much for that info, it is what I suspected might be the case. It needs fixing because at the moment I cannot set the RF output level correctly above about 1.5MHz.

I have not yet fully investigated the fault but I will do as you suggest and check it with my oscilloscope and report back

Alan.

wd40addict · 31st Jan 2018, 10:08 am

On my HF135 there is also a wide variation on range F, but there is enough range to always be able to set to the red line. This gives 10mV RMS into 75R load with 'output' set to 10 and 'attenuator' set to -20dB.

29th Jan 2018, 10:48 pm	#1
a_strong Pentode Join Date: Feb 2007 Location: South Yorkshire, UK. Posts: 134	AVO HF135 - Setting RF Level Fault.... I have recently purchased an AVO HF135 which is very clean and tidy but appears to have a fault on on of its ranges. Although the Set RF Level control seems to work on other ranges I am unable to set it up properly on Range F, the 1-3MHz range. The attached photos may explain the problem. The RF Level control is at minimum and Band F is selected. The Function switch is set to CW. At 1MHZ the reading on the RF Level meter is about 15% of FSD. At 2MHz the reading on the RF Level meter is about 90% of FSD. At 3MHz the reading on the RF Level meter is over 100% of FSD. I would be interested to hear from anyone who might have experienced a similar problem on this or any other range or has any ideas about what may be causing this problem. I have the original Operating Instructions but I have been unable to find any Servicing information anywhere. Thanks in anticipation. This effect is only on Range F and all other ranges behave as you might expect. Attached Thumbnails

30th Jan 2018, 9:29 am	#2
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,990	Re: AVO HF135 - Setting RF Level Fault.... Can't help with your problem but you may be interested to know this model is a re cased Taylor 68AM from when AVO took over Taylor Instruments. __________________ Stephen _________"It`s only an old telly" ___

30th Jan 2018, 10:15 am	#3
karesz* Heptode Join Date: Jun 2010 Location: Zurich, Switzerland Posts: 538	Re: AVO HF135 - Setting RF Level Fault.... HTML Code: Although the Set RF Level control seems to work Means it please that the real RF-output is correct or is varying in same character? https://www.vintage-radio.net/forum/...ad.php?t=59275 I don't have an HF135, but I think that the solution is by search for contact problems in Fr.-range select switch (i.e. output coupling coil)-if the oscillator level itself is not so bad variing_can you check it with an oscilloscope please?

30th Jan 2018, 12:53 pm	#4
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: AVO HF135 - Setting RF Level Fault.... I have the HF135 and mine seems to be similar on range F.There is a fair degree of o/put variation on that range. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

30th Jan 2018, 5:09 pm	#5
a_strong Pentode Join Date: Feb 2007 Location: South Yorkshire, UK. Posts: 134	Re: AVO HF135 - Setting RF Level Fault.... Thanks very much for that info, it is what I suspected might be the case. It needs fixing because at the moment I cannot set the RF output level correctly above about 1.5MHz. I have not yet fully investigated the fault but I will do as you suggest and check it with my oscilloscope and report back Alan.

31st Jan 2018, 10:08 am	#6
wd40addict Octode Join Date: May 2009 Location: Stevenage, Herts. UK. Posts: 1,518	Re: AVO HF135 - Setting RF Level Fault.... On my HF135 there is also a wide variation on range F, but there is enough range to always be able to set to the red line. This gives 10mV RMS into 75R load with 'output' set to 10 and 'attenuator' set to -20dB.