Effect of removing valve from circuit? - UK Vintage Radio Repair and Restoration Discussion Forum

initialsbb · 29th Sep 2019, 3:28 pm

I am converting a Bell & Howell 642 projector amplifier for guitar use.
Circuit diagram is attached.
Part of the circuit is an oscillator used to power the projector's exciter lamp - I plan to remove V7 and associated components to keep things neater (and cooler)
V7 has it's own heater supply so no problem from that perspective, but could removing this valve have any adverse affect on the rest of the circuit?
I have compared voltages with those on the circuit diagram (for the 644 model)
and they are fine as is the bias on V5 and V6 (well V5 is slightly "hot" but replacing the old bias resistors and caps should take care of that)
I'm sorry if it's too basic a question, but I'm going round in circles with this!

paulsherwin · 29th Sep 2019, 3:58 pm

I can't see any potential problems.

Herald1360 · 29th Sep 2019, 4:46 pm

The only effect it may have is a slight increase in HT voltage from the lower load on the supply. Very doubtful that this would be a problem as such.

initialsbb · 29th Sep 2019, 4:49 pm

Thank you for the reassurance!
It sounds fantastic by the way!

29th Sep 2019, 3:28 pm	#1
initialsbb Triode Join Date: Mar 2019 Location: Inverness, Scotland, UK. Posts: 25	Effect of removing valve from circuit? I am converting a Bell & Howell 642 projector amplifier for guitar use. Circuit diagram is attached. Part of the circuit is an oscillator used to power the projector's exciter lamp - I plan to remove V7 and associated components to keep things neater (and cooler) V7 has it's own heater supply so no problem from that perspective, but could removing this valve have any adverse affect on the rest of the circuit? I have compared voltages with those on the circuit diagram (for the 644 model) and they are fine as is the bias on V5 and V6 (well V5 is slightly "hot" but replacing the old bias resistors and caps should take care of that) I'm sorry if it's too basic a question, but I'm going round in circles with this! Attached Thumbnails

29th Sep 2019, 3:58 pm	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,946	Re: Effect of removing valve from circuit? I can't see any potential problems.

29th Sep 2019, 4:46 pm	#3
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Effect of removing valve from circuit? The only effect it may have is a slight increase in HT voltage from the lower load on the supply. Very doubtful that this would be a problem as such. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

29th Sep 2019, 4:49 pm	#4
initialsbb Triode Join Date: Mar 2019 Location: Inverness, Scotland, UK. Posts: 25	Re: Effect of removing valve from circuit? Thank you for the reassurance! It sounds fantastic by the way!